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  <title>this指向 - Knowledge</title>
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  <style>
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    #safearea {
  display: none;
}
:root {
  --color-site-body: #f4f4f4;
  --color-site-bg: #f4f4f4;
  --color-site-inner: #fff;
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  --color-h2: #3a3a3a;
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  --color-h4: #444;
  --color-h5: #555;
  --color-h6: #666;
  --color-p: #444;
  --color-list: #666;
  --color-list-hl: #30ad91;
  --color-meta: #888;
  --color-read-bkg: #e0d8c8;
  --color-read-post: #f8f1e2;
  --color-copyright-bkg: #f5f5f5;
}
* {
  box-sizing: border-box;
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  outline: none;
  margin: 0;
  padding: 0;
}
*::-webkit-scrollbar {
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}
*::-webkit-scrollbar-track-piece {
  background: transparent;
}
*::-webkit-scrollbar-thumb {
  background: #3dd9b6;
  cursor: pointer;
  border-radius: 2px;
  -webkit-border-radius: 2px;
}
*::-webkit-scrollbar-thumb:hover {
  background: #ff5722;
}
html {
  color: var(--color-text);
  width: 100%;
  height: 100%;
  font-family: UbuntuMono, "Varela Round", "PingFang SC", "Microsoft YaHei", Helvetica, Arial, Menlo, Monaco, monospace, sans-serif;
  font-size: 16px;
}
html >::-webkit-scrollbar {
  height: 4px;
  width: 4px;
}
html >::-webkit-scrollbar-track-piece {
  background: transparent;
}
html >::-webkit-scrollbar-thumb {
  background: #54b5a0 linear-gradient(45deg, rgba(255,255,255,0.4) 25%, transparent 25%, transparent 50%, rgba(255,255,255,0.4) 50%, rgba(255,255,255,0.4) 75%, transparent 75%, transparent);
  cursor: pointer;
  border-radius: 2px;
  -webkit-border-radius: 2px;
}
html >::-webkit-scrollbar-thumb:hover {
  background: #54b5a0 linear-gradient(45deg, rgba(255,255,255,0.4) 25%, transparent 25%, transparent 50%, rgba(255,255,255,0.4) 50%, rgba(255,255,255,0.4) 75%, transparent 75%, transparent);
}
body {
  background-color: var(--color-site-body);
  text-rendering: optimizelegibility;
  -webkit-tap-highlight-color: rgba(0,0,0,0);
  line-height: 1.6;
  -webkit-text-size-adjust: 100%;
  -ms-text-size-adjust: 100%;
}
body.modal-active {
  overflow: hidden;
}
@media screen and (max-width: 680px) {
  body.modal-active {
    position: fixed;
    top: 0;
    right: 0;
    bottom: 0;
    left: 0;
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}
a {
  color: #2092ec;
  cursor: pointer;
  text-decoration: none;
  transition: all 0.28s ease;
  -webkit-transition: all 0.28s ease;
  -khtml-transition: all 0.28s ease;
  -moz-transition: all 0.28s ease;
  -o-transition: all 0.28s ease;
  -ms-transition: all 0.28s ease;
}
a:hover {
  color: #ff5722;
}
a:active,
a:hover {
  outline: 0;
}
ul,
ol {
  padding-left: 0;
}
ul li,
ol li {
  list-style: none;
}
header {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: block;
}
img {
  border: 0;
  background: none;
  max-width: 100%;
}
svg:not(:root) {
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}
hr {
  -moz-box-sizing: content-box;
  box-sizing: content-box;
  -webkit-box-sizing: content-box;
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  height: 0;
  border: 0;
  border-radius: 1px;
  -webkit-border-radius: 1px;
  border-bottom: 1px solid rgba(68,68,68,0.1);
}
button,
input {
  color: inherit;
  font: inherit;
  margin: 0;
}
button {
  overflow: visible;
  text-transform: none;
  -webkit-appearance: button;
  cursor: pointer;
}
@supports (backdrop-filter: blur(20px)) {
  .blur {
    background: rgba(255,255,255,0.9) !important;
    backdrop-filter: saturate(200%) blur(20px);
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}
.shadow {
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  -webkit-box-shadow: 0 1px 2px 0px rgba(0,0,0,0.1);
}
.shadow.floatable {
  transition: all 0.28s ease;
  -webkit-transition: all 0.28s ease;
  -khtml-transition: all 0.28s ease;
  -moz-transition: all 0.28s ease;
  -o-transition: all 0.28s ease;
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}
.shadow.floatable:hover {
  box-shadow: 0 2px 4px 0px rgba(0,0,0,0.1), 0 4px 8px 0px rgba(0,0,0,0.1), 0 8px 16px 0px rgba(0,0,0,0.1);
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}
#l_cover {
  min-height: 64px;
}
.cover-wrapper {
  top: 0;
  left: 0;
  max-width: 100%;
  height: 100vh;
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: -ms-flexbox /* TWEENER - IE 10 */;
  display: -webkit-flex /* NEW - Chrome */;
  display: flex /* NEW, Spec - Opera 12.1, Firefox 20+ */;
  display: flex;
  flex-wrap: nowrap;
  -webkit-flex-wrap: nowrap;
  -khtml-flex-wrap: nowrap;
  -moz-flex-wrap: nowrap;
  -o-flex-wrap: nowrap;
  -ms-flex-wrap: nowrap;
  -webkit-box-direction: normal;
  -moz-box-direction: normal;
  -webkit-box-orient: vertical;
  -moz-box-orient: vertical;
  -webkit-flex-direction: column;
  -ms-flex-direction: column;
  flex-direction: column;
  align-items: center;
  align-self: center;
  align-content: center;
  color: var(--color-site-inner);
  padding: 0 16px;
  user-select: none;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  position: relative;
  overflow: hidden;
  margin-bottom: -100px;
}
.cover-wrapper .cover-bg {
  position: absolute;
  width: 100%;
  height: 100%;
  background-position: center;
  background-size: cover;
  -webkit-background-size: cover;
  -moz-background-size: cover;
}
.cover-wrapper .cover-bg.lazyload:not(.loaded) {
  opacity: 0;
  -webkit-opacity: 0;
  -moz-opacity: 0;
}
.cover-wrapper .cover-bg.lazyload.loaded {
  animation-delay: 0s;
  animation-duration: 0.5s;
  animation-fill-mode: forwards;
  animation-timing-function: ease-out;
  animation-name: fadeIn;
}
@-moz-keyframes fadeIn {
  0% {
    opacity: 0;
    -webkit-opacity: 0;
    -moz-opacity: 0;
    filter: blur(12px);
    transform: scale(1.02);
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    -khtml-transform: scale(1.02);
    -moz-transform: scale(1.02);
    -o-transform: scale(1.02);
    -ms-transform: scale(1.02);
  }
  100% {
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
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}
@-webkit-keyframes fadeIn {
  0% {
    opacity: 0;
    -webkit-opacity: 0;
    -moz-opacity: 0;
    filter: blur(12px);
    transform: scale(1.02);
    -webkit-transform: scale(1.02);
    -khtml-transform: scale(1.02);
    -moz-transform: scale(1.02);
    -o-transform: scale(1.02);
    -ms-transform: scale(1.02);
  }
  100% {
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
  }
}
@-o-keyframes fadeIn {
  0% {
    opacity: 0;
    -webkit-opacity: 0;
    -moz-opacity: 0;
    filter: blur(12px);
    transform: scale(1.02);
    -webkit-transform: scale(1.02);
    -khtml-transform: scale(1.02);
    -moz-transform: scale(1.02);
    -o-transform: scale(1.02);
    -ms-transform: scale(1.02);
  }
  100% {
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
  }
}
@keyframes fadeIn {
  0% {
    opacity: 0;
    -webkit-opacity: 0;
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    filter: blur(12px);
    transform: scale(1.02);
    -webkit-transform: scale(1.02);
    -khtml-transform: scale(1.02);
    -moz-transform: scale(1.02);
    -o-transform: scale(1.02);
    -ms-transform: scale(1.02);
  }
  100% {
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
  }
}
.cover-wrapper .cover-body {
  z-index: 1;
  position: relative;
  width: 100%;
  height: 100%;
}
.cover-wrapper#full {
  height: calc(100vh + 100px);
  padding-bottom: 100px;
}
.cover-wrapper#half {
  max-height: 640px;
  min-height: 400px;
  height: calc(36vh - 64px + 200px);
}
.cover-wrapper #scroll-down {
  width: 100%;
  height: 64px;
  position: absolute;
  bottom: 100px;
  text-align: center;
  cursor: pointer;
}
.cover-wrapper #scroll-down .scroll-down-effects {
  color: #fff;
  font-size: 24px;
  line-height: 64px;
  position: absolute;
  width: 24px;
  left: calc(50% - 12px);
  text-shadow: 0 1px 2px rgba(0,0,0,0.1);
  animation: scroll-down-effect 1.5s infinite;
  -webkit-animation: scroll-down-effect 1.5s infinite;
  -khtml-animation: scroll-down-effect 1.5s infinite;
  -moz-animation: scroll-down-effect 1.5s infinite;
  -o-animation: scroll-down-effect 1.5s infinite;
  -ms-animation: scroll-down-effect 1.5s infinite;
}
@-moz-keyframes scroll-down-effect {
  0% {
    top: 0;
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
  }
  50% {
    top: -16px;
    opacity: 0.4;
    -webkit-opacity: 0.4;
    -moz-opacity: 0.4;
  }
  100% {
    top: 0;
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
  }
}
@-webkit-keyframes scroll-down-effect {
  0% {
    top: 0;
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
  }
  50% {
    top: -16px;
    opacity: 0.4;
    -webkit-opacity: 0.4;
    -moz-opacity: 0.4;
  }
  100% {
    top: 0;
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
  }
}
@-o-keyframes scroll-down-effect {
  0% {
    top: 0;
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
  }
  50% {
    top: -16px;
    opacity: 0.4;
    -webkit-opacity: 0.4;
    -moz-opacity: 0.4;
  }
  100% {
    top: 0;
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
  }
}
@keyframes scroll-down-effect {
  0% {
    top: 0;
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
  }
  50% {
    top: -16px;
    opacity: 0.4;
    -webkit-opacity: 0.4;
    -moz-opacity: 0.4;
  }
  100% {
    top: 0;
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
  }
}
.cover-wrapper .cover-body {
  margin-top: 64px;
  margin-bottom: 100px;
}
.cover-wrapper .cover-body,
.cover-wrapper .cover-body .top,
.cover-wrapper .cover-body .bottom {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: -ms-flexbox /* TWEENER - IE 10 */;
  display: -webkit-flex /* NEW - Chrome */;
  display: flex /* NEW, Spec - Opera 12.1, Firefox 20+ */;
  display: flex;
  -webkit-box-direction: normal;
  -moz-box-direction: normal;
  -webkit-box-orient: vertical;
  -moz-box-orient: vertical;
  -webkit-flex-direction: column;
  -ms-flex-direction: column;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  -webkit-justify-content: center;
  -khtml-justify-content: center;
  -moz-justify-content: center;
  -o-justify-content: center;
  -ms-justify-content: center;
  max-width: 100%;
}
.cover-wrapper .cover-body .bottom {
  margin-top: 32px;
}
.cover-wrapper .cover-body .title {
  font-family: "Varela Round", "PingFang SC", "Microsoft YaHei", Helvetica, Arial, Helvetica, monospace;
  font-size: 3.125rem;
  line-height: 1.2;
  text-shadow: 0 1px 2px rgba(0,0,0,0.1);
}
.cover-wrapper .cover-body .subtitle {
  font-size: 20px;
}
.cover-wrapper .cover-body .logo {
  max-height: 120px;
  max-width: calc(100% - 4 * 16px);
}
@media screen and (min-height: 1024px) {
  .cover-wrapper .cover-body .title {
    font-size: 3rem;
  }
  .cover-wrapper .cover-body .subtitle {
    font-size: 1.05rem;
  }
  .cover-wrapper .cover-body .logo {
    max-height: 150px;
  }
}
.cover-wrapper .cover-body .m_search {
  position: relative;
  max-width: calc(100% - 16px);
  width: 320px;
  vertical-align: middle;
}
.cover-wrapper .cover-body .m_search .form {
  position: relative;
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: block;
  width: 100%;
}
.cover-wrapper .cover-body .m_search .icon,
.cover-wrapper .cover-body .m_search .input {
  transition: all 0.28s ease;
  -webkit-transition: all 0.28s ease;
  -khtml-transition: all 0.28s ease;
  -moz-transition: all 0.28s ease;
  -o-transition: all 0.28s ease;
  -ms-transition: all 0.28s ease;
}
.cover-wrapper .cover-body .m_search .icon {
  position: absolute;
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: block;
  line-height: 2.5rem;
  width: 32px;
  top: 0;
  left: 5px;
  color: rgba(68,68,68,0.75);
}
.cover-wrapper .cover-body .m_search .input {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: block;
  height: 2.5rem;
  width: 100%;
  box-shadow: none;
  -webkit-box-shadow: none;
  box-sizing: border-box;
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  font-size: 0.875rem;
  -webkit-appearance: none;
  padding-left: 36px;
  border-radius: 1.4rem;
  -webkit-border-radius: 1.4rem;
  background: rgba(255,255,255,0.6);
  backdrop-filter: blur(10px);
  border: none;
  color: var(--color-text);
}
@media screen and (max-width: 500px) {
  .cover-wrapper .cover-body .m_search .input {
    padding-left: 36px;
  }
}
.cover-wrapper .cover-body .m_search .input:hover {
  background: rgba(255,255,255,0.8);
}
.cover-wrapper .cover-body .m_search .input:focus {
  background: #fff;
}
.cover-wrapper .list-h {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: -ms-flexbox /* TWEENER - IE 10 */;
  display: -webkit-flex /* NEW - Chrome */;
  display: flex /* NEW, Spec - Opera 12.1, Firefox 20+ */;
  display: flex;
  -webkit-box-direction: normal;
  -moz-box-direction: normal;
  -webkit-box-orient: horizontal;
  -moz-box-orient: horizontal;
  -webkit-flex-direction: row;
  -ms-flex-direction: row;
  flex-direction: row;
  flex-wrap: wrap;
  -webkit-flex-wrap: wrap;
  -khtml-flex-wrap: wrap;
  -moz-flex-wrap: wrap;
  -o-flex-wrap: wrap;
  -ms-flex-wrap: wrap;
  align-items: stretch;
  border-radius: 4px;
  -webkit-border-radius: 4px;
  user-select: none;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
}
.cover-wrapper .list-h a {
  -webkit-box-flex: 1;
  -moz-box-flex: 1;
  -webkit-flex: 1 0;
  -ms-flex: 1 0;
  flex: 1 0;
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: -ms-flexbox /* TWEENER - IE 10 */;
  display: -webkit-flex /* NEW - Chrome */;
  display: flex /* NEW, Spec - Opera 12.1, Firefox 20+ */;
  display: flex;
  font-weight: 600;
}
.cover-wrapper .list-h a img {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: block;
  border-radius: 2px;
  -webkit-border-radius: 2px;
  margin: 4px;
  min-width: 40px;
  max-width: 44px;
}
@media screen and (max-width: 768px) {
  .cover-wrapper .list-h a img {
    min-width: 36px;
    max-width: 40px;
  }
}
@media screen and (max-width: 500px) {
  .cover-wrapper .list-h a img {
    margin: 2px 4px;
    min-width: 32px;
    max-width: 36px;
  }
}
@media screen and (max-width: 375px) {
  .cover-wrapper .list-h a img {
    min-width: 28px;
    max-width: 32px;
  }
}
.cover-wrapper {
  max-width: 100%;
}
.cover-wrapper.search .bottom .menu {
  margin-top: 16px;
}
.cover-wrapper.search .bottom .menu .list-h a {
  white-space: nowrap;
  -webkit-box-direction: normal;
  -moz-box-direction: normal;
  -webkit-box-orient: horizontal;
  -moz-box-orient: horizontal;
  -webkit-flex-direction: row;
  -ms-flex-direction: row;
  flex-direction: row;
  align-items: baseline;
  padding: 2px;
  margin: 4px;
  color: var(--color-site-inner);
  opacity: 0.75;
  -webkit-opacity: 0.75;
  -moz-opacity: 0.75;
  text-shadow: 0 1px 2px rgba(0,0,0,0.05);
  border-bottom: 2px solid transparent;
}
.cover-wrapper.search .bottom .menu .list-h a i {
  margin-right: 4px;
}
.cover-wrapper.search .bottom .menu .list-h a p {
  font-size: 0.9375rem;
}
.cover-wrapper.search .bottom .menu .list-h a:hover,
.cover-wrapper.search .bottom .menu .list-h a.active,
.cover-wrapper.search .bottom .menu .list-h a:active {
  opacity: 1;
  -webkit-opacity: 1;
  -moz-opacity: 1;
  border-bottom: 2px solid var(--color-site-inner);
}
.cover-wrapper.dock .menu,
.cover-wrapper.featured .menu,
.cover-wrapper.focus .menu {
  border-radius: 6px;
  -webkit-border-radius: 6px;
}
.cover-wrapper.dock .menu .list-h a,
.cover-wrapper.featured .menu .list-h a,
.cover-wrapper.focus .menu .list-h a {
  -webkit-box-direction: normal;
  -moz-box-direction: normal;
  -webkit-box-orient: vertical;
  -moz-box-orient: vertical;
  -webkit-flex-direction: column;
  -ms-flex-direction: column;
  flex-direction: column;
  align-items: center;
  padding: 12px;
  line-height: 24px;
  border-radius: 4px;
  -webkit-border-radius: 4px;
  border-bottom: none;
  text-align: center;
  align-content: flex-end;
  color: rgba(68,68,68,0.7);
  font-size: 1.5rem;
}
@media screen and (max-width: 500px) {
  .cover-wrapper.dock .menu .list-h a,
  .cover-wrapper.featured .menu .list-h a,
  .cover-wrapper.focus .menu .list-h a {
    padding: 12px 8px;
  }
}
.cover-wrapper.dock .menu .list-h a i,
.cover-wrapper.featured .menu .list-h a i,
.cover-wrapper.focus .menu .list-h a i {
  margin: 8px;
}
.cover-wrapper.dock .menu .list-h a p,
.cover-wrapper.featured .menu .list-h a p,
.cover-wrapper.focus .menu .list-h a p {
  font-size: 0.875rem;
}
.cover-wrapper.dock .menu .list-h a.active,
.cover-wrapper.featured .menu .list-h a.active,
.cover-wrapper.focus .menu .list-h a.active {
  background: var(--color-card);
  backdrop-filter: none;
}
.cover-wrapper.dock .menu .list-h a.active i,
.cover-wrapper.featured .menu .list-h a.active i,
.cover-wrapper.focus .menu .list-h a.active i,
.cover-wrapper.dock .menu .list-h a.active i+p,
.cover-wrapper.featured .menu .list-h a.active i+p,
.cover-wrapper.focus .menu .list-h a.active i+p {
  color: #3dd9b6;
}
.cover-wrapper.dock .menu .list-h a.active img+p,
.cover-wrapper.featured .menu .list-h a.active img+p,
.cover-wrapper.focus .menu .list-h a.active img+p {
  color: var(--color-text);
}
.cover-wrapper.dock .menu .list-h a:hover,
.cover-wrapper.featured .menu .list-h a:hover,
.cover-wrapper.focus .menu .list-h a:hover {
  background: var(--color-card);
}
.cover-wrapper.dock .top {
  margin-bottom: 48px;
}
.cover-wrapper.dock .menu {
  background: rgba(255,255,255,0.5);
  position: absolute;
  bottom: 0;
  max-width: 100%;
}
.cover-wrapper.dock .menu .list-h {
  flex-wrap: nowrap;
  -webkit-flex-wrap: nowrap;
  -khtml-flex-wrap: nowrap;
  -moz-flex-wrap: nowrap;
  -o-flex-wrap: nowrap;
  -ms-flex-wrap: nowrap;
  margin: 4px;
}
.cover-wrapper.dock .menu .list-h a+a {
  margin-left: 4px;
}
@media screen and (max-width: 500px) {
  .cover-wrapper.dock .menu .list-h {
    overflow-x: scroll;
  }
  .cover-wrapper.dock .menu .list-h::-webkit-scrollbar {
    height: 0;
    width: 0;
  }
  .cover-wrapper.dock .menu .list-h::-webkit-scrollbar-track-piece {
    background: transparent;
  }
  .cover-wrapper.dock .menu .list-h::-webkit-scrollbar-thumb {
    background: #3dd9b6;
    cursor: pointer;
    border-radius: 0;
    -webkit-border-radius: 0;
  }
  .cover-wrapper.dock .menu .list-h::-webkit-scrollbar-thumb:hover {
    background: #ff5722;
  }
}
@supports (backdrop-filter: blur(20px)) {
  .cover-wrapper.dock .menu {
    background: rgba(255,255,255,0.5);
    backdrop-filter: saturate(200%) blur(20px);
  }
}
@font-face {
  font-family: 'UbuntuMono';
  src: url("https://unpkg.com/volantis-static@0.0.1654736714924/media/fonts/UbuntuMono/UbuntuMono-Regular.ttf");
  font-weight: 'normal';
  font-style: 'normal';
  font-display: swap;
}
@font-face {
  font-family: 'Varela Round';
  src: url("https://unpkg.com/volantis-static@0.0.1654736714924/media/fonts/VarelaRound/VarelaRound-Regular.ttf");
  font-weight: 'normal';
  font-style: 'normal';
  font-display: swap;
}
.l_header {
  position: fixed;
  z-index: 1000;
  top: 0;
  width: 100%;
  height: 64px;
  background: var(--color-card);
  box-shadow: 0 1px 2px 0px rgba(0,0,0,0.1);
  -webkit-box-shadow: 0 1px 2px 0px rgba(0,0,0,0.1);
}
.l_header.auto {
  transition: opacity 0.4s ease;
  -webkit-transition: opacity 0.4s ease;
  -khtml-transition: opacity 0.4s ease;
  -moz-transition: opacity 0.4s ease;
  -o-transition: opacity 0.4s ease;
  -ms-transition: opacity 0.4s ease;
  visibility: hidden;
}
.l_header.auto.show {
  opacity: 1 !important;
  -webkit-opacity: 1 !important;
  -moz-opacity: 1 !important;
  visibility: visible;
}
.l_header .container {
  margin-left: 16px;
  margin-right: 16px;
}
.l_header #wrapper {
  height: 100%;
  user-select: none;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
}
.l_header #wrapper .nav-main,
.l_header #wrapper .nav-sub {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: -ms-flexbox /* TWEENER - IE 10 */;
  display: -webkit-flex /* NEW - Chrome */;
  display: flex /* NEW, Spec - Opera 12.1, Firefox 20+ */;
  display: flex;
  flex-wrap: nowrap;
  -webkit-flex-wrap: nowrap;
  -khtml-flex-wrap: nowrap;
  -moz-flex-wrap: nowrap;
  -o-flex-wrap: nowrap;
  -ms-flex-wrap: nowrap;
  justify-content: space-between;
  -webkit-justify-content: space-between;
  -khtml-justify-content: space-between;
  -moz-justify-content: space-between;
  -o-justify-content: space-between;
  -ms-justify-content: space-between;
  align-items: center;
}
.l_header #wrapper .nav-main {
  transition: all 0.28s ease;
  -webkit-transition: all 0.28s ease;
  -khtml-transition: all 0.28s ease;
  -moz-transition: all 0.28s ease;
  -o-transition: all 0.28s ease;
  -ms-transition: all 0.28s ease;
}
.l_header #wrapper.sub .nav-main {
  transform: translateY(-64px);
  -webkit-transform: translateY(-64px);
  -khtml-transform: translateY(-64px);
  -moz-transform: translateY(-64px);
  -o-transform: translateY(-64px);
  -ms-transform: translateY(-64px);
}
.l_header #wrapper .nav-sub {
  transition: all 0.28s ease;
  -webkit-transition: all 0.28s ease;
  -khtml-transition: all 0.28s ease;
  -moz-transition: all 0.28s ease;
  -o-transition: all 0.28s ease;
  -ms-transition: all 0.28s ease;
  opacity: 0;
  -webkit-opacity: 0;
  -moz-opacity: 0;
  height: 64px;
  width: calc(100% - 2 * 16px);
  position: absolute;
}
.l_header #wrapper .nav-sub ::-webkit-scrollbar {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: none;
}
@media screen and (min-width: 2048px) {
  .l_header #wrapper .nav-sub {
    max-width: 55vw;
    margin: auto;
  }
}
.l_header #wrapper.sub .nav-sub {
  opacity: 1;
  -webkit-opacity: 1;
  -moz-opacity: 1;
}
.l_header #wrapper .title {
  position: relative;
  color: var(--color-text);
  padding-left: 24px;
  max-height: 64px;
}
.l_header #wrapper .nav-main .title {
  white-space: nowrap;
  overflow: hidden;
  text-overflow: ellipsis;
  flex-shrink: 0;
  line-height: 64px;
  padding: 0 24px;
  font-size: 1.25rem;
  font-family: "Varela Round", "PingFang SC", "Microsoft YaHei", Helvetica, Arial, Helvetica, monospace;
}
.l_header #wrapper .nav-main .title img {
  height: 64px;
}
.l_header .nav-sub {
  max-width: 1080px;
  margin: auto;
}
.l_header .nav-sub .title {
  font-weight: bold;
  font-family: UbuntuMono, "Varela Round", "PingFang SC", "Microsoft YaHei", Helvetica, Arial, Menlo, Monaco, monospace, sans-serif;
  line-height: 1.2;
  max-height: 64px;
  white-space: normal;
  flex-shrink: 1;
}
.l_header .switcher {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: none;
  line-height: 64px;
  align-items: center;
}
.l_header .switcher .s-toc {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: none;
}
@media screen and (max-width: 768px) {
  .l_header .switcher .s-toc {
    display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
    display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
    display: -ms-flexbox /* TWEENER - IE 10 */;
    display: -webkit-flex /* NEW - Chrome */;
    display: flex /* NEW, Spec - Opera 12.1, Firefox 20+ */;
    display: flex;
  }
}
.l_header .switcher >li {
  height: 48px;
  transition: all 0.28s ease;
  -webkit-transition: all 0.28s ease;
  -khtml-transition: all 0.28s ease;
  -moz-transition: all 0.28s ease;
  -o-transition: all 0.28s ease;
  -ms-transition: all 0.28s ease;
  margin: 2px;
}
@media screen and (max-width: 500px) {
  .l_header .switcher >li {
    margin: 0 1px;
    height: 48px;
  }
}
.l_header .switcher >li >a {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: -ms-flexbox /* TWEENER - IE 10 */;
  display: -webkit-flex /* NEW - Chrome */;
  display: flex /* NEW, Spec - Opera 12.1, Firefox 20+ */;
  display: flex;
  justify-content: center;
  -webkit-justify-content: center;
  -khtml-justify-content: center;
  -moz-justify-content: center;
  -o-justify-content: center;
  -ms-justify-content: center;
  align-items: center;
  width: 48px;
  height: 48px;
  padding: 0.85em 1.1em;
  border-radius: 100px;
  -webkit-border-radius: 100px;
  border: none;
  transition: all 0.28s ease;
  -webkit-transition: all 0.28s ease;
  -khtml-transition: all 0.28s ease;
  -moz-transition: all 0.28s ease;
  -o-transition: all 0.28s ease;
  -ms-transition: all 0.28s ease;
  color: #3dd9b6;
}
.l_header .switcher >li >a:hover {
  border: none;
}
.l_header .switcher >li >a.active,
.l_header .switcher >li >a:active {
  border: none;
  background: var(--color-site-bg);
}
@media screen and (max-width: 500px) {
  .l_header .switcher >li >a {
    width: 36px;
    height: 48px;
  }
}
.l_header .nav-sub .switcher {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: -ms-flexbox /* TWEENER - IE 10 */;
  display: -webkit-flex /* NEW - Chrome */;
  display: flex /* NEW, Spec - Opera 12.1, Firefox 20+ */;
  display: flex;
}
.l_header .m_search {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: -ms-flexbox /* TWEENER - IE 10 */;
  display: -webkit-flex /* NEW - Chrome */;
  display: flex /* NEW, Spec - Opera 12.1, Firefox 20+ */;
  display: flex;
  height: 64px;
  width: 240px;
  transition: all 0.28s ease;
  -webkit-transition: all 0.28s ease;
  -khtml-transition: all 0.28s ease;
  -moz-transition: all 0.28s ease;
  -o-transition: all 0.28s ease;
  -ms-transition: all 0.28s ease;
}
@media screen and (max-width: 1024px) {
  .l_header .m_search {
    width: 44px;
    min-width: 44px;
  }
  .l_header .m_search input::placeholder {
    opacity: 0;
    -webkit-opacity: 0;
    -moz-opacity: 0;
  }
  .l_header .m_search:hover {
    width: 240px;
  }
  .l_header .m_search:hover input::placeholder {
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
  }
}
@media screen and (min-width: 500px) {
  .l_header .m_search:hover .input {
    width: 100%;
  }
  .l_header .m_search:hover .input::placeholder {
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
  }
}
@media screen and (max-width: 500px) {
  .l_header .m_search {
    min-width: 0;
  }
  .l_header .m_search input::placeholder {
    opacity: 1;
    -webkit-opacity: 1;
    -moz-opacity: 1;
  }
}
.l_header .m_search .form {
  position: relative;
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: -ms-flexbox /* TWEENER - IE 10 */;
  display: -webkit-flex /* NEW - Chrome */;
  display: flex /* NEW, Spec - Opera 12.1, Firefox 20+ */;
  display: flex;
  width: 100%;
  align-items: center;
}
.l_header .m_search .icon {
  position: absolute;
  width: 36px;
  left: 5px;
  color: var(--color-meta);
}
@media screen and (max-width: 500px) {
  .l_header .m_search .icon {
    display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
    display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
    display: none;
  }
}
.l_header .m_search .input {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: block;
  padding-top: 8px;
  padding-bottom: 8px;
  line-height: 1.3;
  width: 100%;
  color: var(--color-text);
  background: #fafafa;
  box-shadow: none;
  -webkit-box-shadow: none;
  box-sizing: border-box;
  -webkit-box-sizing: border-box;
  -moz-box-sizing: border-box;
  padding-left: 40px;
  font-size: 0.875rem;
  border-radius: 8px;
  -webkit-border-radius: 8px;
  border: none;
  transition: all 0.28s ease;
  -webkit-transition: all 0.28s ease;
  -khtml-transition: all 0.28s ease;
  -moz-transition: all 0.28s ease;
  -o-transition: all 0.28s ease;
  -ms-transition: all 0.28s ease;
}
@media screen and (min-width: 500px) {
  .l_header .m_search .input:focus {
    box-shadow: 0 4px 8px 0px rgba(0,0,0,0.1);
    -webkit-box-shadow: 0 4px 8px 0px rgba(0,0,0,0.1);
  }
}
@media screen and (max-width: 500px) {
  .l_header .m_search .input {
    background: var(--color-block);
    padding-left: 8px;
    border: none;
  }
  .l_header .m_search .input:hover,
  .l_header .m_search .input:focus {
    border: none;
  }
}
@media (max-width: 500px) {
  .l_header .m_search {
    left: 0;
    width: 0;
    overflow: hidden;
    position: absolute;
    background: #fff;
    transition: all 0.28s ease;
    -webkit-transition: all 0.28s ease;
    -khtml-transition: all 0.28s ease;
    -moz-transition: all 0.28s ease;
    -o-transition: all 0.28s ease;
    -ms-transition: all 0.28s ease;
  }
  .l_header .m_search .input {
    border-radius: 32px;
    -webkit-border-radius: 32px;
    margin-left: 16px;
    padding-left: 16px;
  }
  .l_header.z_search-open .m_search {
    width: 100%;
  }
  .l_header.z_search-open .m_search .input {
    width: calc(100% - 120px);
  }
}
ul.m-pc >li>a {
  color: inherit;
  border-bottom: 2px solid transparent;
}
ul.m-pc >li>a:active,
ul.m-pc >li>a.active {
  border-bottom: 2px solid #3dd9b6;
}
ul.m-pc li:hover >ul.list-v,
ul.list-v li:hover >ul.list-v {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: block;
}
ul.nav-list-h {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: -ms-flexbox /* TWEENER - IE 10 */;
  display: -webkit-flex /* NEW - Chrome */;
  display: flex /* NEW, Spec - Opera 12.1, Firefox 20+ */;
  display: flex;
  align-items: stretch;
}
ul.nav-list-h>li {
  position: relative;
  justify-content: center;
  -webkit-justify-content: center;
  -khtml-justify-content: center;
  -moz-justify-content: center;
  -o-justify-content: center;
  -ms-justify-content: center;
  height: 100%;
  line-height: 2.4;
  border-radius: 4px;
  -webkit-border-radius: 4px;
}
ul.nav-list-h>li >a {
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
  font-weight: 600;
}
ul.list-v {
  z-index: 1;
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: none;
  position: absolute;
  background: var(--color-card);
  box-shadow: 0 2px 4px 0px rgba(0,0,0,0.08), 0 4px 8px 0px rgba(0,0,0,0.08), 0 8px 16px 0px rgba(0,0,0,0.08);
  -webkit-box-shadow: 0 2px 4px 0px rgba(0,0,0,0.08), 0 4px 8px 0px rgba(0,0,0,0.08), 0 8px 16px 0px rgba(0,0,0,0.08);
  margin-top: -6px;
  border-radius: 4px;
  -webkit-border-radius: 4px;
  padding: 8px 0;
}
ul.list-v.show {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: block;
}
ul.list-v hr {
  margin-top: 8px;
  margin-bottom: 8px;
}
ul.list-v >li {
  white-space: nowrap;
  word-break: keep-all;
}
ul.list-v >li.header {
  font-size: 0.78125rem;
  font-weight: bold;
  line-height: 2em;
  color: var(--color-meta);
  margin: 8px 16px 4px;
}
ul.list-v >li.header i {
  margin-right: 8px;
}
ul.list-v >li ul {
  margin-left: 0;
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: none;
  margin-top: -40px;
}
ul.list-v .aplayer-container {
  min-height: 64px;
  padding: 6px 16px;
}
ul.list-v >li>a {
  transition: all 0.28s ease;
  -webkit-transition: all 0.28s ease;
  -khtml-transition: all 0.28s ease;
  -moz-transition: all 0.28s ease;
  -o-transition: all 0.28s ease;
  -ms-transition: all 0.28s ease;
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: block;
  color: var(--color-list);
  font-size: 0.875rem;
  font-weight: bold;
  line-height: 36px;
  padding: 0 20px 0 16px;
  text-overflow: ellipsis;
  margin: 0 4px;
  border-radius: 4px;
  -webkit-border-radius: 4px;
}
@media screen and (max-width: 1024px) {
  ul.list-v >li>a {
    line-height: 40px;
  }
}
ul.list-v >li>a >i {
  margin-right: 8px;
}
ul.list-v >li>a:active,
ul.list-v >li>a.active {
  color: var(--color-list-hl);
}
ul.list-v >li>a:hover {
  color: var(--color-list-hl);
  background: var(--color-site-bg);
}
.l_header .menu >ul>li>a {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: block;
  padding: 0 8px;
}
.l_header .menu >ul>li>a >i {
  margin-right: 4px;
}
.l_header ul.nav-list-h>li {
  color: var(--color-list);
  line-height: 64px;
}
.l_header ul.nav-list-h>li >a {
  max-height: 64px;
  overflow: hidden;
  color: inherit;
}
.l_header ul.nav-list-h>li >a:active,
.l_header ul.nav-list-h>li >a.active {
  color: #3dd9b6;
}
.l_header ul.nav-list-h>li:hover>a {
  color: var(--color-list-hl);
}
.l_header ul.nav-list-h>li i.music {
  animation: rotate-effect 1.5s linear infinite;
  -webkit-animation: rotate-effect 1.5s linear infinite;
  -khtml-animation: rotate-effect 1.5s linear infinite;
  -moz-animation: rotate-effect 1.5s linear infinite;
  -o-animation: rotate-effect 1.5s linear infinite;
  -ms-animation: rotate-effect 1.5s linear infinite;
}
@-moz-keyframes rotate-effect {
  0% {
    transform: rotate(0);
    -webkit-transform: rotate(0);
    -khtml-transform: rotate(0);
    -moz-transform: rotate(0);
    -o-transform: rotate(0);
    -ms-transform: rotate(0);
  }
  25% {
    transform: rotate(90deg);
    -webkit-transform: rotate(90deg);
    -khtml-transform: rotate(90deg);
    -moz-transform: rotate(90deg);
    -o-transform: rotate(90deg);
    -ms-transform: rotate(90deg);
  }
  50% {
    transform: rotate(180deg);
    -webkit-transform: rotate(180deg);
    -khtml-transform: rotate(180deg);
    -moz-transform: rotate(180deg);
    -o-transform: rotate(180deg);
    -ms-transform: rotate(180deg);
  }
  75% {
    transform: rotate(270deg);
    -webkit-transform: rotate(270deg);
    -khtml-transform: rotate(270deg);
    -moz-transform: rotate(270deg);
    -o-transform: rotate(270deg);
    -ms-transform: rotate(270deg);
  }
  100% {
    transform: rotate(360deg);
    -webkit-transform: rotate(360deg);
    -khtml-transform: rotate(360deg);
    -moz-transform: rotate(360deg);
    -o-transform: rotate(360deg);
    -ms-transform: rotate(360deg);
  }
}
@-webkit-keyframes rotate-effect {
  0% {
    transform: rotate(0);
    -webkit-transform: rotate(0);
    -khtml-transform: rotate(0);
    -moz-transform: rotate(0);
    -o-transform: rotate(0);
    -ms-transform: rotate(0);
  }
  25% {
    transform: rotate(90deg);
    -webkit-transform: rotate(90deg);
    -khtml-transform: rotate(90deg);
    -moz-transform: rotate(90deg);
    -o-transform: rotate(90deg);
    -ms-transform: rotate(90deg);
  }
  50% {
    transform: rotate(180deg);
    -webkit-transform: rotate(180deg);
    -khtml-transform: rotate(180deg);
    -moz-transform: rotate(180deg);
    -o-transform: rotate(180deg);
    -ms-transform: rotate(180deg);
  }
  75% {
    transform: rotate(270deg);
    -webkit-transform: rotate(270deg);
    -khtml-transform: rotate(270deg);
    -moz-transform: rotate(270deg);
    -o-transform: rotate(270deg);
    -ms-transform: rotate(270deg);
  }
  100% {
    transform: rotate(360deg);
    -webkit-transform: rotate(360deg);
    -khtml-transform: rotate(360deg);
    -moz-transform: rotate(360deg);
    -o-transform: rotate(360deg);
    -ms-transform: rotate(360deg);
  }
}
@-o-keyframes rotate-effect {
  0% {
    transform: rotate(0);
    -webkit-transform: rotate(0);
    -khtml-transform: rotate(0);
    -moz-transform: rotate(0);
    -o-transform: rotate(0);
    -ms-transform: rotate(0);
  }
  25% {
    transform: rotate(90deg);
    -webkit-transform: rotate(90deg);
    -khtml-transform: rotate(90deg);
    -moz-transform: rotate(90deg);
    -o-transform: rotate(90deg);
    -ms-transform: rotate(90deg);
  }
  50% {
    transform: rotate(180deg);
    -webkit-transform: rotate(180deg);
    -khtml-transform: rotate(180deg);
    -moz-transform: rotate(180deg);
    -o-transform: rotate(180deg);
    -ms-transform: rotate(180deg);
  }
  75% {
    transform: rotate(270deg);
    -webkit-transform: rotate(270deg);
    -khtml-transform: rotate(270deg);
    -moz-transform: rotate(270deg);
    -o-transform: rotate(270deg);
    -ms-transform: rotate(270deg);
  }
  100% {
    transform: rotate(360deg);
    -webkit-transform: rotate(360deg);
    -khtml-transform: rotate(360deg);
    -moz-transform: rotate(360deg);
    -o-transform: rotate(360deg);
    -ms-transform: rotate(360deg);
  }
}
@keyframes rotate-effect {
  0% {
    transform: rotate(0);
    -webkit-transform: rotate(0);
    -khtml-transform: rotate(0);
    -moz-transform: rotate(0);
    -o-transform: rotate(0);
    -ms-transform: rotate(0);
  }
  25% {
    transform: rotate(90deg);
    -webkit-transform: rotate(90deg);
    -khtml-transform: rotate(90deg);
    -moz-transform: rotate(90deg);
    -o-transform: rotate(90deg);
    -ms-transform: rotate(90deg);
  }
  50% {
    transform: rotate(180deg);
    -webkit-transform: rotate(180deg);
    -khtml-transform: rotate(180deg);
    -moz-transform: rotate(180deg);
    -o-transform: rotate(180deg);
    -ms-transform: rotate(180deg);
  }
  75% {
    transform: rotate(270deg);
    -webkit-transform: rotate(270deg);
    -khtml-transform: rotate(270deg);
    -moz-transform: rotate(270deg);
    -o-transform: rotate(270deg);
    -ms-transform: rotate(270deg);
  }
  100% {
    transform: rotate(360deg);
    -webkit-transform: rotate(360deg);
    -khtml-transform: rotate(360deg);
    -moz-transform: rotate(360deg);
    -o-transform: rotate(360deg);
    -ms-transform: rotate(360deg);
  }
}
.menu-phone li ul.list-v {
  right: calc(100% - 0.5 * 16px);
}
.menu-phone li ul.list-v ul {
  right: calc(100% - 0.5 * 16px);
}
#wrapper {
  max-width: 1080px;
  margin: auto;
}
@media screen and (min-width: 2048px) {
  #wrapper {
    max-width: 55vw;
  }
}
#wrapper .menu {
  -webkit-box-flex: 1;
  -moz-box-flex: 1;
  -webkit-flex: 1 1;
  -ms-flex: 1 1;
  flex: 1 1;
  margin: 0 16px 0 0;
}
#wrapper .menu .list-v ul {
  left: calc(100% - 0.5 * 16px);
}
.menu-phone {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: none;
  margin-top: 16px;
  right: 8px;
  transition: all 0.28s ease;
  -webkit-transition: all 0.28s ease;
  -khtml-transition: all 0.28s ease;
  -moz-transition: all 0.28s ease;
  -o-transition: all 0.28s ease;
  -ms-transition: all 0.28s ease;
}
.menu-phone ul {
  right: calc(100% - 0.5 * 16px);
}
@media screen and (max-width: 500px) {
  .menu-phone {
    display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
    display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
    display: block;
  }
}
.l_header {
  max-width: 65vw;
  left: calc((100% - 65vw) * 0.5);
  border-bottom-left-radius: 8px;
  border-bottom-right-radius: 8px;
}
@media screen and (max-width: 2048px) {
  .l_header {
    max-width: 1112px;
    left: calc((100% - 1112px) * 0.5);
  }
}
@media screen and (max-width: 1112px) {
  .l_header {
    left: 0;
    border-radius: 0;
    -webkit-border-radius: 0;
    max-width: 100%;
  }
}
@media screen and (max-width: 500px) {
  .l_header .container {
    margin-left: 0;
    margin-right: 0;
  }
  .l_header #wrapper .nav-main .title {
    padding-left: 16px;
    padding-right: 16px;
  }
  .l_header #wrapper .nav-sub {
    width: 100%;
  }
  .l_header #wrapper .nav-sub .title {
    overflow-y: scroll;
    margin-top: 2px;
    padding: 8px 16px;
  }
  .l_header #wrapper .switcher {
    display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
    display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
    display: -ms-flexbox /* TWEENER - IE 10 */;
    display: -webkit-flex /* NEW - Chrome */;
    display: flex /* NEW, Spec - Opera 12.1, Firefox 20+ */;
    display: flex;
    margin-right: 8px;
  }
  .l_header .menu {
    display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
    display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
    display: none;
  }
}
@media screen and (max-width: 500px) {
  .list-v li {
    max-width: 270px;
  }
}
#u-search {
  display: -webkit-box /* OLD - iOS 6-, Safari 3.1-6 */;
  display: -moz-box /* OLD - Firefox 19- (buggy but mostly works) */;
  display: none;
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 100%;
  padding: 60px 20px;
  z-index: 1001;
}
@media screen and (max-width: 680px) {
  #u-search {
    padding: 0px;
  }
}

  </style>
  <link rel="stylesheet" href="/css/style.css" media="print" onload="this.media='all';this.onload=null">
  <noscript><link rel="stylesheet" href="/css/style.css"></noscript>
  
<script>
if (/*@cc_on!@*/false || (!!window.MSInputMethodContext && !!document.documentMode))
    document.write(
	'<style>'+
		'html{'+
			'overflow-x: hidden !important;'+
			'overflow-y: hidden !important;'+
		'}'+
		'.kill-ie{'+
			'text-align:center;'+
			'height: 100%;'+
			'margin-top: 15%;'+
			'margin-bottom: 5500%;'+
		'}'+
    '.kill-t{'+
      'font-size: 2rem;'+
    '}'+
    '.kill-c{'+
      'font-size: 1.2rem;'+
    '}'+
		'#l_header,#l_body{'+
			'display: none;'+
		'}'+
	'</style>'+
    '<div class="kill-ie">'+
        `<span class="kill-t"><b>Sorry, your browser cannot access this site</b></span><br/>`+
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    '</div>');
</script>


<noscript>
	<style>
		html{
			overflow-x: hidden !important;
			overflow-y: hidden !important;
		}
		.kill-noscript{
			text-align:center;
			height: 100%;
			margin-top: 15%;
			margin-bottom: 5500%;
		}
    .kill-t{
      font-size: 2rem;
    }
    .kill-c{
      font-size: 1.2rem;
    }
		#l_header,#l_body{
			display: none;
		}
	</style>
    <div class="kill-noscript">
        <span class="kill-t"><b>Sorry, your browser cannot access this site</b></span><br/>
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        <a target="_blank" rel="noopener" href="https://www.baidu.com/s?wd=启用JavaScript"><strong>Learn more ></strong></a>
    </div>
</noscript>


  <script>
  /************这个文件存放不需要重载的全局变量和全局函数*********/
  window.volantis = {}; // volantis 全局变量
  volantis.debug = "env"; // 调试模式
  volantis.dom = {}; // 页面Dom see: /source/js/app.js etc.

  volantis.GLOBAL_CONFIG ={
    debug: "env",
    cdn: {"js":{"app":"/js/app.js","parallax":"/js/plugins/parallax.js","rightMenu":"/js/plugins/rightMenu.js","rightMenus":"/js/plugins/rightMenus.js","sites":"/js/plugins/tags/sites.js","friends":"/js/plugins/tags/friends.js","contributors":"/js/plugins/tags/contributors.js","search":"/js/search/hexo.js"},"css":{"style":"/css/style.css"}},
    default: {"avatar":"https://unpkg.com/volantis-static@0.0.1654736714924/media/placeholder/avatar/round/3442075.svg","link":"https://unpkg.com/volantis-static@0.0.1654736714924/media/placeholder/link/8f277b4ee0ecd.svg","cover":"https://unpkg.com/volantis-static@0.0.1654736714924/media/placeholder/cover/76b86c0226ffd.svg","image":"https://unpkg.com/volantis-static@0.0.1654736714924/media/placeholder/image/2659360.svg"},
    lastupdate: new Date(1739433735785),
    sidebar: {
      for_page: ["blogger","category","tagcloud","donate"],
      for_post: ["toc"],
      webinfo: {
        lastupd: {
          enable: true,
          friendlyShow: true
        },
        runtime: {
          data: "2020/01/01",
          unit: "天"
        }
      }
    },
    plugins: {
      message: {"enable":true,"css":"https://unpkg.com/volantis-static@0.0.1654736714924/libs/izitoast/dist/css/iziToast.min.css","js":"https://unpkg.com/volantis-static@0.0.1654736714924/libs/izitoast/dist/js/iziToast.min.js","icon":{"default":"fa-solid fa-info-circle light-blue","quection":"fa-solid fa-question-circle light-blue"},"time":{"default":5000,"quection":20000},"position":"topRight","transitionIn":"bounceInLeft","transitionOut":"fadeOutRight","titleColor":"var(--color-text)","messageColor":"var(--color-text)","backgroundColor":"var(--color-card)","zindex":2147483647,"copyright":{"enable":true,"title":"知识共享许可协议","message":"请遵守 CC BY-NC-SA 4.0 协议。","icon":"far fa-copyright light-blue"},"aplayer":{"enable":true,"play":"fa-solid fa-play","pause":"fa-solid fa-pause"},"rightmenu":{"enable":true,"notice":true}},
      fancybox: {"css":"https://unpkg.com/volantis-static@0.0.1654736714924/libs/@fancyapps/ui/dist/fancybox.css","js":"https://unpkg.com/volantis-static@0.0.1654736714924/libs/@fancyapps/ui/dist/fancybox.umd.js"},
      
      
      
    }
  }

  /******************** volantis.EventListener ********************************/
  // 事件监听器 see: /source/js/app.js
  volantis.EventListener = {}
  // 这里存放pjax切换页面时将被移除的事件监听器
  volantis.EventListener.list = []
  //构造方法
  function volantisEventListener(type, f, ele) {
    this.type = type
    this.f = f
    this.ele = ele
  }
  // 移除事件监听器
  volantis.EventListener.remove = () => {
    volantis.EventListener.list.forEach(function (i) {
      i.ele.removeEventListener(i.type, i.f, false)
    })
    volantis.EventListener.list = []
  }
  /******************** volantis.dom.$ ********************************/
  // 注：这里没有选择器，也没有forEach一次只处理一个dom，这里重新封装主题常用的dom方法，返回的是dom对象，对象包含了以下方法，同时保留dom的原生API
  function volantisDom(ele) {
    if (!ele) ele = document.createElement("div")
    this.ele = ele;
    // ==============================================================
    this.ele.find = (c) => {
      let q = this.ele.querySelector(c)
      if (q)
        return new volantisDom(q)
    }
    // ==============================================================
    this.ele.hasClass = (c) => {
      return this.ele.className.match(new RegExp('(\\s|^)' + c + '(\\s|$)'));
    }
    this.ele.addClass = (c) => {
      this.ele.classList.add(c);
      return this.ele
    }
    this.ele.removeClass = (c) => {
      this.ele.classList.remove(c);
      return this.ele
    }
    this.ele.toggleClass = (c) => {
      if (this.ele.hasClass(c)) {
        this.ele.removeClass(c)
      } else {
        this.ele.addClass(c)
      }
      return this.ele
    }
    // ==============================================================
    // 参数 r 为 true 表示pjax切换页面时事件监听器将被移除，false不移除
    this.ele.on = (c, f, r = 1) => {
      this.ele.addEventListener(c, f, false)
      if (r) {
        volantis.EventListener.list.push(new volantisEventListener(c, f, this.ele))
      }
      return this.ele
    }
    this.ele.click = (f, r) => {
      this.ele.on("click", f, r)
      return this.ele
    }
    this.ele.scroll = (f, r) => {
      this.ele.on("scroll", f, r)
      return this.ele
    }
    // ==============================================================
    this.ele.html = (c) => {
      // if(c=== undefined){
      //   return this.ele.innerHTML
      // }else{
      this.ele.innerHTML = c
      return this.ele
      // }
    }
    // ==============================================================
    this.ele.hide = (c) => {
      this.ele.style.display = "none"
      return this.ele
    }
    this.ele.show = (c) => {
      this.ele.style.display = "block"
      return this.ele
    }
    // ==============================================================
    return this.ele
  }
  volantis.dom.$ = (ele) => {
    return !!ele ? new volantisDom(ele) : null;
  }
  /******************** RunItem ********************************/
  function RunItem() {
    this.list = []; // 存放回调函数
    this.start = () => {
      for (var i = 0; i < this.list.length; i++) {
        this.list[i].run();
      }
    };
    this.push = (fn, name, setRequestAnimationFrame = true) => {
      let myfn = fn
      if (setRequestAnimationFrame) {
        myfn = ()=>{
          volantis.requestAnimationFrame(fn)
        }
      }
      var f = new Item(myfn, name);
      this.list.push(f);
    };
    this.remove = (name) =>{
      for (let index = 0; index < this.list.length; index++) {
        const e = this.list[index];
        if (e.name == name) {
          this.list.splice(index,1);
        }
      }
    }
    // 构造一个可以run的对象
    function Item(fn, name) {
      // 函数名称
      this.name = name || fn.name;
      // run方法
      this.run = () => {
        try {
          fn()
        } catch (error) {
          console.log(error);
        }
      };
    }
  }
  /******************** Pjax ********************************/
  // /layout/_plugins/pjax/index.ejs
  // volantis.pjax.send(callBack[,"callBackName"]) 传入pjax:send回调函数
  // volantis.pjax.push(callBack[,"callBackName"]) 传入pjax:complete回调函数
  // volantis.pjax.error(callBack[,"callBackName"]) 传入pjax:error回调函数
  volantis.pjax = {};
  volantis.pjax.method = {
    complete: new RunItem(),
    error: new RunItem(),
    send: new RunItem(),
  };
  volantis.pjax = Object.assign(volantis.pjax, {
    push: volantis.pjax.method.complete.push,
    error: volantis.pjax.method.error.push,
    send: volantis.pjax.method.send.push,
  });
  /******************** RightMenu ********************************/
  // volantis.rightmenu.handle(callBack[,"callBackName"]) 外部菜单项控制
  // 可在 volantis.mouseEvent 处获取右键事件
  volantis.rightmenu = {};
  volantis.rightmenu.method = {
    handle: new RunItem(),
  }
  volantis.rightmenu = Object.assign(volantis.rightmenu, {
    handle: volantis.rightmenu.method.handle.push,
  });
  /********************  Dark Mode  ********************************/
  // /layout/_partial/scripts/darkmode.ejs
  // volantis.dark.mode 当前模式 dark or light
  // volantis.dark.toggle() 暗黑模式触发器
  // volantis.dark.push(callBack[,"callBackName"]) 传入触发器回调函数
  volantis.dark = {};
  volantis.dark.method = {
    toggle: new RunItem(),
  };
  volantis.dark = Object.assign(volantis.dark, {
    push: volantis.dark.method.toggle.push,
  });
  /********************  Message  ********************************/
  // VolantisApp.message
  /********************  isMobile  ********************************/
  // /source/js/app.js
  // volantis.isMobile
  // volantis.isMobileOld
  /********************脚本动态加载函数********************************/
  // volantis.js(src, cb)  cb 可以传入onload回调函数 或者 JSON对象 例如: volantis.js("src", ()=>{}) 或 volantis.js("src", {defer:true,onload:()=>{}})
  // volantis.css(src)

  // 返回Promise对象，如下方法同步加载资源，这利于处理文件资源之间的依赖关系，例如：APlayer 需要在 MetingJS 之前加载
  // (async () => {
  //     await volantis.js("...theme.plugins.aplayer.js.aplayer...")
  //     await volantis.js("...theme.plugins.aplayer.js.meting...")
  // })();

  // 已经加入了setTimeout
  volantis.js = (src, cb) => {
    return new Promise(resolve => {
      setTimeout(function () {
        var HEAD = document.getElementsByTagName("head")[0] || document.documentElement;
        var script = document.createElement("script");
        script.setAttribute("type", "text/javascript");
        if (cb) {
          if (JSON.stringify(cb)) {
            for (let p in cb) {
              if (p == "onload") {
                script[p] = () => {
                  cb[p]()
                  resolve()
                }
              } else {
                script[p] = cb[p]
                script.onload = resolve
              }
            }
          } else {
            script.onload = () => {
              cb()
              resolve()
            };
          }
        } else {
          script.onload = resolve
        }
        script.setAttribute("src", src);
        HEAD.appendChild(script);
      });
    });
  }
  volantis.css = (src) => {
    return new Promise(resolve => {
      setTimeout(function () {
        var link = document.createElement('link');
        link.rel = "stylesheet";
        link.href = src;
        link.onload = resolve;
        document.getElementsByTagName("head")[0].appendChild(link);
      });
    });
  }
  /********************按需加载的插件********************************/
  // volantis.import.jQuery().then(()=>{})
  volantis.import = {
    jQuery: () => {
      if (typeof jQuery == "undefined") {
        return volantis.js("https://unpkg.com/volantis-static@0.0.1654736714924/libs/jquery/dist/jquery.min.js")
      } else {
        return new Promise(resolve => {
          resolve()
        });
      }
    }
  }
  /********************** requestAnimationFrame ********************************/
  // 1、requestAnimationFrame 会把每一帧中的所有 DOM 操作集中起来，在一次重绘或回流中就完成，并且重绘或回流的时间间隔紧紧跟随浏览器的刷新频率，一般来说，这个频率为每秒60帧。
  // 2、在隐藏或不可见的元素中，requestAnimationFrame 将不会进行重绘或回流，这当然就意味着更少的的 cpu，gpu 和内存使用量。
  volantis.requestAnimationFrame = (fn)=>{
    if (!window.requestAnimationFrame) {
      window.requestAnimationFrame = window.requestAnimationFrame || window.mozRequestAnimationFrame || window.webkitRequestAnimationFrame;
    }
    window.requestAnimationFrame(fn)
  }
  /************************ layoutHelper *****************************************/
  volantis.layoutHelper = (helper, html, opt)=>{
    opt = Object.assign({clean:false, pjax:true}, opt)
    function myhelper(helper, html, clean) {
      volantis.tempDiv = document.createElement("div");
      volantis.tempDiv.innerHTML = html;
      let layoutHelper = document.querySelector("#layoutHelper-"+helper)
      if (layoutHelper) {
        if (clean) {
          layoutHelper.innerHTML = ""
        }
        layoutHelper.append(volantis.tempDiv);
      }
    }
    myhelper(helper, html, opt.clean)
    if (opt.pjax) {
      volantis.pjax.push(()=>{
        myhelper(helper, html, opt.clean)
      },"layoutHelper-"+helper)
    }
  }
  /****************************** 滚动事件处理 ****************************************/
  volantis.scroll = {
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    <h2 id="this指向案例-1-10"><a href="#this指向案例-1-10" class="headerlink" title="this指向案例 1-10"></a>this指向案例 1-10</h2><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br><span class="line">128</span><br><span class="line">129</span><br><span class="line">130</span><br><span class="line">131</span><br><span class="line">132</span><br><span class="line">133</span><br><span class="line">134</span><br><span class="line">135</span><br><span class="line">136</span><br><span class="line">137</span><br><span class="line">138</span><br><span class="line">139</span><br><span class="line">140</span><br><span class="line">141</span><br><span class="line">142</span><br><span class="line">143</span><br><span class="line">144</span><br><span class="line">145</span><br><span class="line">146</span><br><span class="line">147</span><br><span class="line">148</span><br><span class="line">149</span><br><span class="line">150</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">//https:wenku.baidu.com/view/1c35a4e32fc58bd63186bceb19e8b8f67c1cefd2.html</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 1、 非严格模式下，print()为默认绑定，this指向window</span></span><br><span class="line"><span class="comment">// 在预编译过程中，foo和print函数会存放在全局中(即window对象上)</span></span><br><span class="line"><span class="keyword">var</span> foo = <span class="number">123</span>; <span class="comment">// window.foo = 123</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">print</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">this</span>.<span class="property">foo</span> = <span class="number">234</span>;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>); <span class="comment">// Window</span></span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(foo); <span class="comment">// 234  console.log(window.foo)</span></span><br><span class="line">&#125;</span><br><span class="line"><span class="title function_">print</span>(); <span class="comment">// window.print()</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 2、 开启严格模式后，函数内部this指向undefined，但全局对象window</span></span><br><span class="line">(<span class="string">&#x27;use strict&#x27;</span>);</span><br><span class="line"><span class="keyword">var</span> foo = <span class="number">123</span>;</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">print</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;print this is&#x27;</span>, <span class="variable language_">this</span>); <span class="comment">// Window</span></span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">window</span>.<span class="property">foo</span>); <span class="comment">// 123</span></span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">foo</span>); <span class="comment">// Cannot read properties of undefined</span></span><br><span class="line">&#125;</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;global this is&#x27;</span>, <span class="variable language_">this</span>); <span class="comment">// undefined</span></span><br><span class="line"><span class="title function_">print</span>();</span><br><span class="line"><span class="comment">// 3、 let和const定义的变量存在暂时性死区，而且不会挂载到window对象上，</span></span><br><span class="line"><span class="comment">// 因此print中是无法获取a和b的</span></span><br><span class="line"><span class="keyword">var</span> a = <span class="number">1</span>;</span><br><span class="line"><span class="keyword">const</span> b = <span class="number">2</span>;</span><br><span class="line"><span class="keyword">var</span> c = <span class="number">3</span>;</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">print</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>); <span class="comment">// undefined</span></span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">b</span>); <span class="comment">// undefined</span></span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">c</span>); <span class="comment">// 3</span></span><br><span class="line">&#125;</span><br><span class="line"><span class="title function_">print</span>();</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>); <span class="comment">// undefined</span></span><br><span class="line"><span class="comment">// 4、 对象内执行</span></span><br><span class="line"><span class="comment">// foo虽然在obj的bar函数中，但foo函数仍然是独立运行的，</span></span><br><span class="line"><span class="comment">// foo中的this依旧指向window对象</span></span><br><span class="line">a = <span class="number">1</span>;</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">foo</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> obj = &#123;</span><br><span class="line">  <span class="attr">a</span>: <span class="number">10</span>,</span><br><span class="line">  <span class="title function_">bar</span>(<span class="params"></span>) &#123;</span><br><span class="line">    <span class="title function_">foo</span>(); <span class="comment">// 1</span></span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line">obj.<span class="title function_">bar</span>();</span><br><span class="line"><span class="comment">// 5、 函数内执行，注意：不要看出闭包了</span></span><br><span class="line"><span class="keyword">var</span> a = <span class="number">1</span>;</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">outer</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="keyword">var</span> a = <span class="number">2</span>;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>); <span class="comment">// 1</span></span><br><span class="line">  <span class="keyword">function</span> <span class="title function_">inner</span>(<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>); <span class="comment">// 1</span></span><br><span class="line">  &#125;</span><br><span class="line">  <span class="title function_">inner</span>();</span><br><span class="line">&#125;</span><br><span class="line"><span class="title function_">outer</span>();</span><br><span class="line"><span class="comment">// 6、 自执行函数</span></span><br><span class="line"><span class="comment">// 默认请情况下，自执行函数的this指向window</span></span><br><span class="line"><span class="comment">// 自执行函数只要运行到就会运行，并且只会运行一次，this指向window</span></span><br><span class="line">a = <span class="number">1</span>;</span><br><span class="line">(<span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>); <span class="comment">// Window</span></span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>); <span class="comment">// 1</span></span><br><span class="line">&#125;)();</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">bar</span>(<span class="params"></span>) &#123;</span><br><span class="line">  b = <span class="number">2</span>;</span><br><span class="line">  (<span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>); <span class="comment">// Window</span></span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">b</span>); <span class="comment">// 2 b是imply global，会挂载到window上</span></span><br><span class="line">  &#125;)();</span><br><span class="line">&#125;</span><br><span class="line"><span class="title function_">bar</span>();</span><br><span class="line"><span class="comment">// 7、 隐式绑定</span></span><br><span class="line"><span class="comment">// 函数的调用是在某个对象上触发的，即调用位置存在上下文对象，</span></span><br><span class="line"><span class="comment">// 通俗点说就是XXX.func()这种调用模式。</span></span><br><span class="line"><span class="comment">// 此时func的this指向XXX，但如果存在链式调用，例如XXX.YYY.ZZZ.func</span></span><br><span class="line"><span class="comment">// 记住一个原则：this永远指向最后调用它的那个对象</span></span><br><span class="line"><span class="keyword">var</span> a = <span class="number">1</span>;</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">foo</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> obj = &#123; <span class="attr">a</span>: <span class="number">2</span>, foo &#125;;</span><br><span class="line"><span class="title function_">foo</span>(); <span class="comment">// 默认绑定，打印 1</span></span><br><span class="line">obj.<span class="title function_">foo</span>(); <span class="comment">// 隐式绑定，打印 2</span></span><br><span class="line"><span class="comment">// obj是通过var定义的，obj会挂载到window之上的，</span></span><br><span class="line"><span class="comment">// obj.foo()就相当于window.obj.foo()，</span></span><br><span class="line"><span class="comment">// 这也印证了this永远指向最后调用它的那个对象规则</span></span><br><span class="line"><span class="comment">// 8、 隐式绑定的丢失</span></span><br><span class="line"><span class="comment">// 隐式绑定可是个调皮的东西，一不小心它就会发生绑定的丢失。</span></span><br><span class="line"><span class="comment">// 一般会有两种丢失：</span></span><br><span class="line"><span class="comment">// 使用另一个变量作为函数别名，之后使用别名执行函数</span></span><br><span class="line"><span class="comment">// 将函数作为参数传递是会被隐式赋值</span></span><br><span class="line"><span class="comment">// 隐式绑定丢失之后，this的指向会启用默认绑定</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 取函数别名</span></span><br><span class="line">a = <span class="number">1</span>;</span><br><span class="line"><span class="keyword">var</span> obj = &#123;</span><br><span class="line">  <span class="attr">a</span>: <span class="number">2</span>,</span><br><span class="line">  <span class="title function_">foo</span>(<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">var</span> foo = obj.<span class="property">foo</span>;</span><br><span class="line">obj.<span class="title function_">foo</span>(); <span class="comment">// 2</span></span><br><span class="line"><span class="title function_">foo</span>(); <span class="comment">// 1</span></span><br><span class="line"><span class="comment">// JavaScript对于引用类型，其地址指针存放在栈内存中，</span></span><br><span class="line"><span class="comment">// 真正的本体是存放在堆内存中的</span></span><br><span class="line"><span class="comment">// 上面将obj.foo()赋值给foo，就是将foo也指向了obj.foo所指向的堆内存，</span></span><br><span class="line"><span class="comment">// 此后再执行foo，相当于直接执行的堆内存的函数，与obj无关，foo为默认绑定。</span></span><br><span class="line"><span class="comment">// 笼统的记，只要fn前面上面都没有，肯定不是隐式绑定</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 不要把这里理解成window.foo执行，如果foo为let/const定义，</span></span><br><span class="line"><span class="comment">// foo不会挂载到window上，但不会影响最后的打印</span></span><br><span class="line"><span class="comment">// 9、 取函数别名</span></span><br><span class="line"><span class="comment">// 如果取函数别名没有发生在全局，而是发生在对象之中，又会是怎样的结果呢？</span></span><br><span class="line"><span class="keyword">var</span> obj = &#123;</span><br><span class="line">  <span class="attr">a</span>: <span class="number">1</span>,</span><br><span class="line">  <span class="title function_">foo</span>(<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">var</span> a = <span class="number">2</span>;</span><br><span class="line"><span class="keyword">var</span> foo = obj.<span class="property">foo</span>;</span><br><span class="line"><span class="keyword">var</span> obj2 = &#123; <span class="attr">a</span>: <span class="number">3</span>, <span class="attr">foo</span>: obj.<span class="property">foo</span> &#125;;</span><br><span class="line">obj.<span class="title function_">foo</span>(); <span class="comment">// 1</span></span><br><span class="line"><span class="title function_">foo</span>(); <span class="comment">// 2</span></span><br><span class="line">obj2.<span class="title function_">foo</span>(); <span class="comment">// 3</span></span><br><span class="line"><span class="comment">// obj2.foo指向了obj.foo的堆内存，</span></span><br><span class="line"><span class="comment">// 此后执行与obj无关(除非使用call/apply改变this指向)</span></span><br><span class="line"><span class="comment">// 10、 函数作为参数传递</span></span><br><span class="line"><span class="comment">// 用函数预编译的知识来解答这个问题：函数预编译四部曲前两步分别是：</span></span><br><span class="line"><span class="comment">// 1、找形参和变量声明，值赋予undefined</span></span><br><span class="line"><span class="comment">// 2、将形参和实参相统一，也就是将实参的值赋予形参</span></span><br><span class="line"><span class="comment">// obj.foo作为实参，在预编译时将其值赋值给形参fn，</span></span><br><span class="line"><span class="comment">// 是将obj.foo指向的地址赋给了fn, 此后fn执行不会与obj产生任务关系。</span></span><br><span class="line"><span class="comment">// fn为默认绑定</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">foo</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>); <span class="comment">// 2</span></span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">doFoo</span>(<span class="params">fn</span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;this&#x27;</span>, <span class="variable language_">this</span>); <span class="comment">// Window</span></span><br><span class="line">  <span class="title function_">fn</span>();</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> obj = &#123; <span class="attr">a</span>: <span class="number">1</span>, foo &#125;;</span><br><span class="line"><span class="keyword">var</span> a = <span class="number">2</span>;</span><br><span class="line"><span class="title function_">doFoo</span>(obj.<span class="property">foo</span>);</span><br><span class="line"></span><br></pre></td></tr></table></figure>

<h2 id="this指向案例-11-20"><a href="#this指向案例-11-20" class="headerlink" title="this指向案例 11-20"></a>this指向案例 11-20</h2><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br><span class="line">128</span><br><span class="line">129</span><br><span class="line">130</span><br><span class="line">131</span><br><span class="line">132</span><br><span class="line">133</span><br><span class="line">134</span><br><span class="line">135</span><br><span class="line">136</span><br><span class="line">137</span><br><span class="line">138</span><br><span class="line">139</span><br><span class="line">140</span><br><span class="line">141</span><br><span class="line">142</span><br><span class="line">143</span><br><span class="line">144</span><br><span class="line">145</span><br><span class="line">146</span><br><span class="line">147</span><br><span class="line">148</span><br><span class="line">149</span><br><span class="line">150</span><br><span class="line">151</span><br><span class="line">152</span><br><span class="line">153</span><br><span class="line">154</span><br><span class="line">155</span><br><span class="line">156</span><br><span class="line">157</span><br><span class="line">158</span><br><span class="line">159</span><br><span class="line">160</span><br><span class="line">161</span><br><span class="line">162</span><br><span class="line">163</span><br><span class="line">164</span><br><span class="line">165</span><br><span class="line">166</span><br><span class="line">167</span><br><span class="line">168</span><br><span class="line">169</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// this指向案例 11-20</span></span><br><span class="line"><span class="comment">// 11、 函数作为参数传递</span></span><br><span class="line"><span class="comment">// 当dofoo不在window上执行，改为在obj2中执行</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">foo</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>); <span class="comment">// 2</span></span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">doFoo</span>(<span class="params">fn</span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;this&#x27;</span>, <span class="variable language_">this</span>); <span class="comment">// &#123;a: 3, doFoo: f&#125;</span></span><br><span class="line">  <span class="title function_">fn</span>();</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> obj = &#123; <span class="attr">a</span>: <span class="number">1</span>, foo &#125;;</span><br><span class="line"><span class="keyword">var</span> a = <span class="number">2</span>;</span><br><span class="line"><span class="keyword">var</span> obj2 = &#123; <span class="attr">a</span>: <span class="number">3</span>, doFoo &#125;;</span><br><span class="line">obj2.<span class="title function_">doFoo</span>(obj.<span class="property">foo</span>);</span><br><span class="line"><span class="comment">// fn()没有于obj2产生联系，默认绑定，打印2</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 12、 回调函数</span></span><br><span class="line"><span class="keyword">var</span> name = <span class="string">&#x27;zcxiaobao&#x27;</span>;</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">introduce</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;Hello, My name is&#x27;</span>, <span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">const</span> <span class="title class_">Tom</span> = &#123;</span><br><span class="line">  <span class="attr">name</span>: <span class="string">&#x27;TOM&#x27;</span>,</span><br><span class="line">  <span class="attr">introduce</span>: <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="built_in">setTimeout</span>(<span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>);</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;Hello, My name is&#x27;</span>, <span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    &#125;);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">const</span> <span class="title class_">Mary</span> = &#123;</span><br><span class="line">  <span class="attr">name</span>: <span class="string">&#x27;Mary&#x27;</span>,</span><br><span class="line">  introduce</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">const</span> <span class="title class_">Lisa</span> = &#123;</span><br><span class="line">  <span class="attr">name</span>: <span class="string">&#x27;lisa&#x27;</span>,</span><br><span class="line">  introduce</span><br><span class="line">&#125;;</span><br><span class="line"><span class="title class_">Tom</span>.<span class="title function_">introduce</span>(); <span class="comment">// Window zcxiaobao</span></span><br><span class="line"><span class="built_in">setTimeout</span>(<span class="title class_">Mary</span>.<span class="property">introduce</span>, <span class="number">1000</span>); <span class="comment">// zcxiaobao</span></span><br><span class="line"><span class="built_in">setTimeout</span>(<span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">  <span class="title class_">Lisa</span>.<span class="title function_">introduce</span>(); <span class="comment">// lisa</span></span><br><span class="line">&#125;, <span class="number">2000</span>);</span><br><span class="line"><span class="comment">// setTimeout是异步调用的，只有当满足条件并且同步代码执行完毕后，</span></span><br><span class="line"><span class="comment">// 才执行它的回调函数</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 13、如果我们想在setTimeout或setInterval中使用外界的this，</span></span><br><span class="line"><span class="comment">// 需要提前存储一下，避免this的丢失</span></span><br><span class="line"><span class="comment">// 当然还有方式是可以将setTimeout改为箭头函数，</span></span><br><span class="line"><span class="comment">// 这样的话，this就可以指向上一层</span></span><br><span class="line"><span class="keyword">var</span> name = <span class="string">&#x27;zcxiaobao&#x27;</span>;</span><br><span class="line"><span class="keyword">const</span> <span class="title class_">Tom</span> = &#123;</span><br><span class="line">  <span class="attr">name</span>: <span class="string">&#x27;TOM&#x27;</span>,</span><br><span class="line">  <span class="attr">introduce</span>: <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    _self = <span class="variable language_">this</span>;</span><br><span class="line">    <span class="built_in">setTimeout</span>(<span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(_self);</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;Hello, My name is&#x27;</span>, _self.<span class="property">name</span>);</span><br><span class="line">    &#125;);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line"><span class="title class_">Tom</span>.<span class="title function_">introduce</span>(); <span class="comment">// &#123;name: &#x27;TOM&#x27;, introduce: f &#125; TOM</span></span><br><span class="line"><span class="comment">// 14、隐式绑定丢失综合题</span></span><br><span class="line">name = <span class="string">&#x27;javascript&#x27;</span>;</span><br><span class="line"><span class="keyword">let</span> obj = &#123;</span><br><span class="line">  <span class="attr">name</span>: <span class="string">&#x27;obj&#x27;</span>,</span><br><span class="line">  <span class="title function_">A</span>(<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">this</span>.<span class="property">name</span> += <span class="string">&#x27;this&#x27;</span>;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">  &#125;,</span><br><span class="line">  <span class="title function_">B</span>(<span class="params">f</span>) &#123;</span><br><span class="line">    <span class="variable language_">this</span>.<span class="property">name</span> += <span class="string">&#x27;this&#x27;</span>;</span><br><span class="line">    <span class="title function_">f</span>();</span><br><span class="line">  &#125;,</span><br><span class="line">  <span class="title function_">C</span>(<span class="params"></span>) &#123;</span><br><span class="line">    <span class="built_in">setTimeout</span>(<span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    &#125;, <span class="number">1000</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">let</span> a = obj.<span class="property">A</span>;</span><br><span class="line"><span class="title function_">a</span>(); <span class="comment">// javascriptthis</span></span><br><span class="line">obj.<span class="title function_">B</span>(<span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>); <span class="comment">// javascriptthis</span></span><br><span class="line">&#125;);</span><br><span class="line">obj.<span class="title function_">C</span>(); <span class="comment">// javascriptthis</span></span><br><span class="line"><span class="comment">// 15、显式绑定 比较三种调用方法</span></span><br><span class="line"><span class="comment">// 显式绑定比较好理解，就是通过call()、apply()、bind()等方法，强行改变this指向。</span></span><br><span class="line"><span class="comment">// call()和apply()函数会立即执行</span></span><br><span class="line"><span class="comment">// bind()函数会返回新函数，不会立即执行函数</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">foo</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> obj = &#123; <span class="attr">a</span>: <span class="number">1</span> &#125;;</span><br><span class="line"><span class="keyword">var</span> a = <span class="number">2</span>;</span><br><span class="line"><span class="title function_">foo</span>(); <span class="comment">// 默认绑定 2</span></span><br><span class="line">foo.<span class="title function_">call</span>(obj); <span class="comment">// 显示绑定 1</span></span><br><span class="line">foo.<span class="title function_">apply</span>(obj); <span class="comment">// 显示绑定 1</span></span><br><span class="line">foo.<span class="title function_">bind</span>(obj); <span class="comment">// 显示绑定， 但不会立即执行函数，没有返回值</span></span><br><span class="line"><span class="comment">// 16、发生隐式绑定丢失，通过显示绑定来修正这个问题</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">foo</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">doFoo</span>(<span class="params">fn</span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>);</span><br><span class="line">  fn.<span class="title function_">call</span>(<span class="variable language_">this</span>);</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> obj = &#123; <span class="attr">a</span>: <span class="number">1</span>, foo &#125;;</span><br><span class="line"><span class="keyword">var</span> a = <span class="number">2</span>;</span><br><span class="line">doFoo.<span class="title function_">call</span>(obj, obj.<span class="property">foo</span>); <span class="comment">// &#123; a: 1, foo: f &#125;</span></span><br><span class="line"><span class="comment">// 17、回调函数与call</span></span><br><span class="line"><span class="keyword">var</span> obj1 = &#123;</span><br><span class="line">  <span class="attr">a</span>: <span class="number">1</span></span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">var</span> obj2 = &#123;</span><br><span class="line">  <span class="attr">a</span>: <span class="number">2</span>,</span><br><span class="line">  <span class="attr">bar</span>: <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">  &#125;,</span><br><span class="line">  <span class="attr">foo</span>: <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="built_in">setTimeout</span>(</span><br><span class="line">      <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">        <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>);</span><br><span class="line">        <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">      &#125;.<span class="title function_">call</span>(obj1),</span><br><span class="line">      <span class="number">0</span></span><br><span class="line">    );</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">var</span> a = <span class="number">3</span>;</span><br><span class="line">obj2.<span class="title function_">bar</span>(); <span class="comment">// 2</span></span><br><span class="line">obj2.<span class="title function_">foo</span>(); <span class="comment">// &#123; a: 1 &#125; 1</span></span><br><span class="line"><span class="comment">// 18、注意call位置(1)</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">foo</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> obj = &#123; <span class="attr">a</span>: <span class="number">1</span> &#125;;</span><br><span class="line"><span class="keyword">var</span> a = <span class="number">2</span>;</span><br><span class="line"><span class="title function_">foo</span>(); <span class="comment">// 默认绑定 2</span></span><br><span class="line">foo.<span class="title function_">call</span>(obj); <span class="comment">// 显式绑定 1</span></span><br><span class="line"><span class="title function_">foo</span>().<span class="title function_">call</span>(obj); <span class="comment">// 2 Cannot read properties of undefined(reading &#x27;call&#x27;)</span></span><br><span class="line"><span class="comment">// 19、注意call位置(2)</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">foo</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">  <span class="keyword">return</span> <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>, <span class="string">&#x27;return&#x27;</span>);</span><br><span class="line">  &#125;;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> obj = &#123; <span class="attr">a</span>: <span class="number">1</span> &#125;;</span><br><span class="line"><span class="keyword">var</span> a = <span class="number">2</span>;</span><br><span class="line"><span class="title function_">foo</span>(); <span class="comment">// 默认绑定 2</span></span><br><span class="line">foo.<span class="title function_">call</span>(obj); <span class="comment">// 显式绑定 1</span></span><br><span class="line"><span class="title function_">foo</span>().<span class="title function_">call</span>(obj); <span class="comment">// 2   1 &#x27;return&#x27;</span></span><br><span class="line"><span class="comment">// 注意： 最后有foo().call(obj)有两个函数执行，会打印两个值</span></span><br><span class="line"><span class="comment">// 20、当把call全部换做bind函数，又会有怎样</span></span><br><span class="line"><span class="comment">// call是会立即执行函数，bind会返回一个新函数，但不会执行函数</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">foo</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">  <span class="keyword">return</span> <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>, <span class="string">&#x27;return&#x27;</span>);</span><br><span class="line">  &#125;;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> obj = &#123; <span class="attr">a</span>: <span class="number">1</span> &#125;;</span><br><span class="line"><span class="keyword">var</span> a = <span class="number">2</span>;</span><br><span class="line"><span class="title function_">foo</span>(); <span class="comment">// 默认绑定 2</span></span><br><span class="line">foo.<span class="title function_">bind</span>(obj); <span class="comment">// 返回新函数，不会执行函数，无输出</span></span><br><span class="line"><span class="keyword">const</span> newFoo = foo.<span class="title function_">bind</span>(obj);</span><br><span class="line"><span class="title function_">newFoo</span>(); <span class="comment">// 1</span></span><br><span class="line"><span class="title function_">foo</span>().<span class="title function_">bind</span>(obj); <span class="comment">// 2</span></span><br></pre></td></tr></table></figure>

<h2 id="this指向案例-21-30"><a href="#this指向案例-21-30" class="headerlink" title="this指向案例 21-30"></a>this指向案例 21-30</h2><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br><span class="line">128</span><br><span class="line">129</span><br><span class="line">130</span><br><span class="line">131</span><br><span class="line">132</span><br><span class="line">133</span><br><span class="line">134</span><br><span class="line">135</span><br><span class="line">136</span><br><span class="line">137</span><br><span class="line">138</span><br><span class="line">139</span><br><span class="line">140</span><br><span class="line">141</span><br><span class="line">142</span><br><span class="line">143</span><br><span class="line">144</span><br><span class="line">145</span><br><span class="line">146</span><br><span class="line">147</span><br><span class="line">148</span><br><span class="line">149</span><br><span class="line">150</span><br><span class="line">151</span><br><span class="line">152</span><br><span class="line">153</span><br><span class="line">154</span><br><span class="line">155</span><br><span class="line">156</span><br><span class="line">157</span><br><span class="line">158</span><br><span class="line">159</span><br><span class="line">160</span><br><span class="line">161</span><br><span class="line">162</span><br><span class="line">163</span><br><span class="line">164</span><br><span class="line">165</span><br><span class="line">166</span><br><span class="line">167</span><br><span class="line">168</span><br><span class="line">169</span><br><span class="line">170</span><br><span class="line">171</span><br><span class="line">172</span><br><span class="line">173</span><br><span class="line">174</span><br><span class="line">175</span><br><span class="line">176</span><br><span class="line">177</span><br><span class="line">178</span><br><span class="line">179</span><br><span class="line">180</span><br><span class="line">181</span><br><span class="line">182</span><br><span class="line">183</span><br><span class="line">184</span><br><span class="line">185</span><br><span class="line">186</span><br><span class="line">187</span><br><span class="line">188</span><br><span class="line">189</span><br><span class="line">190</span><br><span class="line">191</span><br><span class="line">192</span><br><span class="line">193</span><br><span class="line">194</span><br><span class="line">195</span><br><span class="line">196</span><br><span class="line">197</span><br><span class="line">198</span><br><span class="line">199</span><br><span class="line">200</span><br><span class="line">201</span><br><span class="line">202</span><br><span class="line">203</span><br><span class="line">204</span><br><span class="line">205</span><br><span class="line">206</span><br><span class="line">207</span><br><span class="line">208</span><br><span class="line">209</span><br><span class="line">210</span><br><span class="line">211</span><br><span class="line">212</span><br><span class="line">213</span><br><span class="line">214</span><br><span class="line">215</span><br><span class="line">216</span><br><span class="line">217</span><br><span class="line">218</span><br><span class="line">219</span><br><span class="line">220</span><br><span class="line">221</span><br><span class="line">222</span><br><span class="line">223</span><br><span class="line">224</span><br><span class="line">225</span><br><span class="line">226</span><br><span class="line">227</span><br><span class="line">228</span><br><span class="line">229</span><br><span class="line">230</span><br><span class="line">231</span><br><span class="line">232</span><br><span class="line">233</span><br><span class="line">234</span><br><span class="line">235</span><br><span class="line">236</span><br><span class="line">237</span><br><span class="line">238</span><br><span class="line">239</span><br><span class="line">240</span><br><span class="line">241</span><br><span class="line">242</span><br><span class="line">243</span><br><span class="line">244</span><br><span class="line">245</span><br><span class="line">246</span><br><span class="line">247</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// this指向案例 21-30</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 21、外层this与内层this</span></span><br><span class="line"><span class="comment">// 如果使用call、bind等修改了外层函数的this，那内层函数的this会受影响吗</span></span><br><span class="line"><span class="comment">// 注意区别箭头函数</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">foo</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">  <span class="keyword">return</span> <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">  &#125;;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> obj = &#123; <span class="attr">a</span>: <span class="number">1</span> &#125;;</span><br><span class="line"><span class="keyword">var</span> a = <span class="number">2</span>;</span><br><span class="line">foo.<span class="title function_">call</span>(obj)(); <span class="comment">// 1   2</span></span><br><span class="line"><span class="comment">// 第一层函数foo通过call将this指向obj，打印1</span></span><br><span class="line"><span class="comment">// 第二层函数为匿名函数，默认绑定，打印2</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 22、对象中的call</span></span><br><span class="line"><span class="keyword">var</span> obj = &#123;</span><br><span class="line">  <span class="attr">a</span>: <span class="string">&#x27;obj&#x27;</span>,</span><br><span class="line">  <span class="attr">foo</span>: <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;foo&#x27;</span>, <span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">    <span class="keyword">return</span> <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span>);</span><br><span class="line">    &#125;;</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">var</span> a = <span class="string">&#x27;window&#x27;</span>;</span><br><span class="line"><span class="keyword">var</span> obj2 = &#123; <span class="attr">a</span>: <span class="string">&#x27;obj2&#x27;</span> &#125;;</span><br><span class="line">obj.<span class="title function_">foo</span>()(); <span class="comment">// &#x27;foo&#x27; obj   window</span></span><br><span class="line">obj.<span class="property">foo</span>.<span class="title function_">call</span>(obj2)(); <span class="comment">// &#x27;foo&#x27; obj2   window</span></span><br><span class="line">obj.<span class="title function_">foo</span>().<span class="title function_">call</span>(obj2); <span class="comment">// &#x27;foo&#x27; obj   obj2</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 23、带参数的call</span></span><br><span class="line"><span class="comment">// 显示绑定一开始讲的时候，就谈过call/apply存在传参差异，</span></span><br><span class="line"><span class="comment">// 那咱们就来传一下参数，看看传完参数的this会是怎么的美妙</span></span><br><span class="line"><span class="keyword">var</span> obj = &#123;</span><br><span class="line">  <span class="attr">a</span>: <span class="number">1</span>,</span><br><span class="line">  <span class="attr">foo</span>: <span class="keyword">function</span> (<span class="params">b</span>) &#123;</span><br><span class="line">    b = b || <span class="variable language_">this</span>.<span class="property">a</span>;</span><br><span class="line">    <span class="keyword">return</span> <span class="keyword">function</span> (<span class="params">c</span>) &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">a</span> + b + c);</span><br><span class="line">    &#125;;</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">var</span> a = <span class="number">2</span>;</span><br><span class="line"><span class="keyword">var</span> obj2 = &#123; <span class="attr">a</span>: <span class="number">3</span> &#125;;</span><br><span class="line">obj.<span class="title function_">foo</span>(a).<span class="title function_">call</span>(obj2, <span class="number">1</span>); <span class="comment">// 3 + 2 + 1 = 6</span></span><br><span class="line"><span class="comment">// obj.foo(a) 这边我们可以推出 b = 2</span></span><br><span class="line"><span class="comment">// 接下来由于return出来的匿名函数指向了obj2，可以推出 a = 3，c = 1</span></span><br><span class="line">obj.<span class="property">foo</span>.<span class="title function_">call</span>(obj2)(<span class="number">1</span>); <span class="comment">// 2 + 3 + 1 = 6</span></span><br><span class="line"><span class="comment">// obj.foo.call(obj2) obj.foo的this指向obj2，未传入参数</span></span><br><span class="line"><span class="comment">// b = this.a = obj2.a = 3；返回匿名函数fn</span></span><br><span class="line"><span class="comment">// 匿名函数fn(1) 可得 c = 1，由于默认绑定，this指向Window，则 a = 2</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 24、显示绑定拓展</span></span><br><span class="line"><span class="comment">// apply求数组最值</span></span><br><span class="line"><span class="comment">// JavaScript中没有给数组提供类似max和min函数，</span></span><br><span class="line"><span class="comment">// 只提供了Max.max/min， 用于求多个数的最值，</span></span><br><span class="line"><span class="comment">// 所以可以借助apply方法，直接传递给Math.max/min</span></span><br><span class="line"><span class="keyword">const</span> arr = [<span class="number">1</span>, <span class="number">10</span>, <span class="number">11</span>, <span class="number">33</span>, <span class="number">4</span>, <span class="number">52</span>, <span class="number">17</span>];</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="title class_">Math</span>.<span class="property">max</span>.<span class="title function_">apply</span>(<span class="title class_">Math</span>, arr)); <span class="comment">// 52</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="title class_">Math</span>.<span class="property">min</span>.<span class="title function_">apply</span>(<span class="title class_">Math</span>, arr)); <span class="comment">// 1</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 类数组转为数组</span></span><br><span class="line"><span class="comment">// ES6未发布之前，没有Array.from方法可以将类数组转为数组，</span></span><br><span class="line"><span class="comment">// 采用Array.prototype.slice.call(arguments)或</span></span><br><span class="line"><span class="comment">// [].slice.call(arguments)将类数组转化为数组</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 数组高阶函数</span></span><br><span class="line"><span class="comment">// 日常编码中，我们会经常用到forEach、map等，</span></span><br><span class="line"><span class="comment">// 但这些数组高阶方法，它们还有第二个参数thisArg，</span></span><br><span class="line"><span class="comment">// 每一个回调函数都是显式绑定在thisArg上的</span></span><br><span class="line"><span class="keyword">const</span> obj = &#123; <span class="attr">a</span>: <span class="number">10</span> &#125;;</span><br><span class="line"><span class="keyword">const</span> array = [<span class="number">1</span>, <span class="number">2</span>, <span class="number">3</span>, <span class="number">4</span>];</span><br><span class="line">array.<span class="title function_">forEach</span>(<span class="keyword">function</span> (<span class="params">val, key</span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">`<span class="subst">$&#123;key&#125;</span>: <span class="subst">$&#123;val&#125;</span> --- <span class="subst">$&#123;<span class="variable language_">this</span>.a&#125;</span>`</span>);</span><br><span class="line">&#125;, obj);</span><br><span class="line"></span><br><span class="line"><span class="comment">// 25、new绑定</span></span><br><span class="line"><span class="comment">// 使用new来构建函数，会执行如下四部操作：</span></span><br><span class="line"><span class="comment">// 1、创建一个空的简单JavaScript对象(即&#123;&#125;)</span></span><br><span class="line"><span class="comment">// 2、为步骤1新创建的对象添加属性__proto__,</span></span><br><span class="line"><span class="comment">// 将该属性链接至构造函数的原型对象；</span></span><br><span class="line"><span class="comment">// 3、将步骤1新创建的对象作为this的上下文；</span></span><br><span class="line"><span class="comment">// 如果该函数没有返回对象，则返回this</span></span><br><span class="line"><span class="comment">// 通过new来调用构造函数，会生成一个新对象，</span></span><br><span class="line"><span class="comment">// 并且把这个新对象绑定为调用函数的this</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">User</span>(<span class="params">name, age</span>) &#123;</span><br><span class="line">  <span class="variable language_">this</span>.<span class="property">name</span> = name;</span><br><span class="line">  <span class="variable language_">this</span>.<span class="property">age</span> = age;</span><br><span class="line">  <span class="variable language_">this</span>.<span class="property">introduce</span> = <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">  &#125;;</span><br><span class="line">  <span class="variable language_">this</span>.<span class="property">howOld</span> = <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="keyword">return</span> <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">age</span>);</span><br><span class="line">    &#125;;</span><br><span class="line">  &#125;;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> name = <span class="string">&#x27;Tom&#x27;</span>;</span><br><span class="line"><span class="keyword">var</span> age = <span class="number">18</span>;</span><br><span class="line"><span class="keyword">var</span> zc = <span class="keyword">new</span> <span class="title class_">User</span>(<span class="string">&#x27;zc&#x27;</span>, <span class="number">24</span>);</span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(zc.<span class="property">name</span>); <span class="comment">// zc</span></span><br><span class="line">zc.<span class="title function_">introduce</span>(); <span class="comment">// zc</span></span><br><span class="line"><span class="comment">// zc是new创建的实例，this指向zc，打印zc</span></span><br><span class="line">zc.<span class="title function_">howOld</span>()(); <span class="comment">// 18</span></span><br><span class="line"><span class="comment">// zc.howOld()返回一个匿名函数，匿名函数为默认绑定</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 26、new界的天王山 （太难了太难了）</span></span><br><span class="line"><span class="comment">// 部分优先级如下：</span></span><br><span class="line"><span class="comment">// new(带参数列表) = 成员访问 = 函数调用 &gt; new(不带参数)</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">Foo</span>(<span class="params"></span>) &#123;</span><br><span class="line">  getName = <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="number">1</span>);</span><br><span class="line">  &#125;;</span><br><span class="line">  <span class="keyword">return</span> <span class="variable language_">this</span>;</span><br><span class="line">&#125;</span><br><span class="line"><span class="title class_">Foo</span>.<span class="property">getName</span> = <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="number">2</span>);</span><br><span class="line">&#125;;</span><br><span class="line"><span class="title class_">Foo</span>.<span class="property"><span class="keyword">prototype</span></span>.<span class="property">getName</span> = <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="number">3</span>);</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">var</span> getName = <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="number">4</span>);</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">getName</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="number">5</span>); <span class="comment">// 在运行了Foo()后，5变为1了</span></span><br><span class="line">&#125;</span><br><span class="line"><span class="comment">// 预编译</span></span><br><span class="line"><span class="comment">// GO = &#123;</span></span><br><span class="line"><span class="comment">//   Foo: fn(Foo),</span></span><br><span class="line"><span class="comment">//   getName: function getName() &#123;</span></span><br><span class="line"><span class="comment">//     console.log(5);</span></span><br><span class="line"><span class="comment">//   &#125;,</span></span><br><span class="line"><span class="comment">// &#125;;</span></span><br><span class="line"><span class="title class_">Foo</span>.<span class="title function_">getName</span>(); <span class="comment">// 2</span></span><br><span class="line"><span class="title function_">getName</span>(); <span class="comment">// 4</span></span><br><span class="line"><span class="title class_">Foo</span>().<span class="title function_">getName</span>(); <span class="comment">// 1 相当于window.getName()</span></span><br><span class="line"><span class="comment">// Foo()执行完后</span></span><br><span class="line"><span class="comment">// 修改全局GO的getName为function()&#123;console.log(1)&#125;</span></span><br><span class="line"><span class="comment">// Foo为默认绑定，this -&gt; window</span></span><br><span class="line"><span class="comment">// return window</span></span><br><span class="line"><span class="title function_">getName</span>(); <span class="comment">// 1</span></span><br><span class="line"><span class="keyword">new</span> <span class="title class_">Foo</span>.<span class="title function_">getName</span>(); <span class="comment">// 2</span></span><br><span class="line"><span class="comment">// 首先从左往右看：new Foo属于不带参数列表的new(优先级19)，</span></span><br><span class="line"><span class="comment">// Foo.getName属于成员访问(优先级20)，</span></span><br><span class="line"><span class="comment">// getName()属于函数调用(优先级20)，同样优先级遵循从左往右执行</span></span><br><span class="line"><span class="comment">// 此时原表达式变为new(Foo.getName)()，其为带参数列表(优先级20)，</span></span><br><span class="line"><span class="comment">// (Foo.getName)()属于函数调用(优先级20)，从左往右执行</span></span><br><span class="line"><span class="keyword">new</span> <span class="title class_">Foo</span>().<span class="title function_">getName</span>(); <span class="comment">// 3</span></span><br><span class="line"><span class="comment">// new Foo()</span></span><br><span class="line"><span class="comment">// Foo.prototype.getName</span></span><br><span class="line"><span class="keyword">new</span> <span class="keyword">new</span> <span class="title class_">Foo</span>().<span class="title function_">getName</span>(); <span class="comment">// 3</span></span><br><span class="line"><span class="comment">// new(new Foo().getName)()</span></span><br><span class="line"><span class="comment">// Foo.prototype.getName()</span></span><br><span class="line"></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;--------------------&#x27;</span>);</span><br><span class="line">foo1 = <span class="keyword">new</span> <span class="title class_">Foo</span>.<span class="title function_">getName</span>(); <span class="comment">// 2</span></span><br><span class="line">foo2 = <span class="keyword">new</span> <span class="keyword">new</span> <span class="title class_">Foo</span>().<span class="title function_">getName</span>(); <span class="comment">// 3</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(foo1.<span class="property">constructor</span>); <span class="comment">// f() &#123;console.log(2)&#125;</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(foo2.<span class="property">constructor</span>); <span class="comment">// f() &#123;console.log(3)&#125;</span></span><br><span class="line"><span class="comment">// new Foo.getName()和new new Foo().getName() 二者区别</span></span><br><span class="line"><span class="comment">// new Foo.getName()的构造函数是Foo.getName</span></span><br><span class="line"><span class="comment">// new new Foo().getName()的构造函数为Foo.prototype.getName</span></span><br><span class="line"><span class="comment">// 27、指向函数定义时的this而非执行时：JavaScript是静态作用域,</span></span><br><span class="line"><span class="comment">// 就是函数定义之后，作用域就定死了，跟他执行时的地方无关</span></span><br><span class="line"><span class="comment">// 对象方法使用箭头函数</span></span><br><span class="line">name = <span class="string">&#x27;tom&#x27;</span>;</span><br><span class="line"><span class="keyword">const</span> obj = &#123;</span><br><span class="line">  <span class="attr">name</span>: <span class="string">&#x27;zc&#x27;</span>,</span><br><span class="line">  <span class="attr">intro</span>: <span class="function">() =&gt;</span> &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;My name is &#x27;</span> + <span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line">obj.<span class="title function_">intro</span>(); <span class="comment">// tom</span></span><br><span class="line"><span class="comment">// 箭头函数的this通过作用域链查到，</span></span><br><span class="line"><span class="comment">// intro函数的上层作用域为window</span></span><br><span class="line"><span class="comment">// 28、箭头函数与普通函数比较</span></span><br><span class="line">name = <span class="string">&#x27;tom&#x27;</span>;</span><br><span class="line"><span class="keyword">const</span> obj = &#123;</span><br><span class="line">  <span class="attr">name</span>: <span class="string">&#x27;zc&#x27;</span>,</span><br><span class="line">  <span class="attr">intro</span>: <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="keyword">return</span> <span class="function">() =&gt;</span> &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;=&gt;&#x27;</span>, <span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    &#125;;</span><br><span class="line">  &#125;,</span><br><span class="line">  <span class="attr">intro2</span>: <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="keyword">return</span> <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="string">&#x27;普通函数&#x27;</span>, <span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    &#125;;</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line">obj.<span class="title function_">intro</span>()(); <span class="comment">// zc</span></span><br><span class="line">obj.<span class="title function_">intro2</span>()(); <span class="comment">// tom</span></span><br><span class="line"><span class="comment">// 29、箭头函数与普通函数的嵌套</span></span><br><span class="line">name = <span class="string">&#x27;window&#x27;</span>;</span><br><span class="line"><span class="keyword">const</span> obj1 = &#123;</span><br><span class="line">  <span class="attr">name</span>: <span class="string">&#x27;obj1&#x27;</span>,</span><br><span class="line">  <span class="attr">intro</span>: <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    <span class="keyword">return</span> <span class="function">() =&gt;</span> &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    &#125;;</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">const</span> obj2 = &#123;</span><br><span class="line">  <span class="attr">name</span>: <span class="string">&#x27;obj2&#x27;</span>,</span><br><span class="line">  <span class="attr">intro</span>: <span class="function">() =&gt;</span> &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    <span class="keyword">return</span> <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    &#125;;</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">const</span> obj3 = &#123;</span><br><span class="line">  <span class="attr">name</span>: <span class="string">&#x27;obj3&#x27;</span>,</span><br><span class="line">  <span class="attr">intro</span>: <span class="function">() =&gt;</span> &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    <span class="keyword">return</span> <span class="function">() =&gt;</span> &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    &#125;;</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line">obj1.<span class="title function_">intro</span>()(); <span class="comment">// obj1 obj1</span></span><br><span class="line">obj2.<span class="title function_">intro</span>()(); <span class="comment">// window window</span></span><br><span class="line">obj3.<span class="title function_">intro</span>()(); <span class="comment">// window window</span></span><br><span class="line"><span class="comment">// 30、new碰上箭头函数</span></span><br><span class="line"><span class="keyword">function</span> <span class="title function_">User</span>(<span class="params">name, age</span>) &#123;</span><br><span class="line">  <span class="variable language_">this</span>.<span class="property">name</span> = name;</span><br><span class="line">  <span class="variable language_">this</span>.<span class="property">age</span> = age;</span><br><span class="line">  <span class="variable language_">this</span>.<span class="property">intro</span> = <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">  &#125;;</span><br><span class="line">  <span class="variable language_">this</span>.<span class="property">howOld</span> = <span class="function">() =&gt;</span> &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">age</span>);</span><br><span class="line">  &#125;;</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> name = <span class="string">&#x27;Tom&#x27;</span>,</span><br><span class="line">  aeg = <span class="number">18</span>;</span><br><span class="line"><span class="keyword">var</span> zc = <span class="keyword">new</span> <span class="title class_">User</span>(<span class="string">&#x27;zc&#x27;</span>, <span class="number">24</span>);</span><br><span class="line">zc.<span class="title function_">intro</span>(); <span class="comment">// zc</span></span><br><span class="line">zc.<span class="title function_">howOld</span>(); <span class="comment">// 24</span></span><br><span class="line"><span class="comment">// howOld为箭头函数this由外层决定，且指向函数定义时的this，</span></span><br><span class="line"><span class="comment">// 外层作用域为User，this指向zc</span></span><br><span class="line"></span><br></pre></td></tr></table></figure>

<h2 id="this指向案例31-N"><a href="#this指向案例31-N" class="headerlink" title="this指向案例31 - N"></a>this指向案例31 - N</h2><figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br><span class="line">2</span><br><span class="line">3</span><br><span class="line">4</span><br><span class="line">5</span><br><span class="line">6</span><br><span class="line">7</span><br><span class="line">8</span><br><span class="line">9</span><br><span class="line">10</span><br><span class="line">11</span><br><span class="line">12</span><br><span class="line">13</span><br><span class="line">14</span><br><span class="line">15</span><br><span class="line">16</span><br><span class="line">17</span><br><span class="line">18</span><br><span class="line">19</span><br><span class="line">20</span><br><span class="line">21</span><br><span class="line">22</span><br><span class="line">23</span><br><span class="line">24</span><br><span class="line">25</span><br><span class="line">26</span><br><span class="line">27</span><br><span class="line">28</span><br><span class="line">29</span><br><span class="line">30</span><br><span class="line">31</span><br><span class="line">32</span><br><span class="line">33</span><br><span class="line">34</span><br><span class="line">35</span><br><span class="line">36</span><br><span class="line">37</span><br><span class="line">38</span><br><span class="line">39</span><br><span class="line">40</span><br><span class="line">41</span><br><span class="line">42</span><br><span class="line">43</span><br><span class="line">44</span><br><span class="line">45</span><br><span class="line">46</span><br><span class="line">47</span><br><span class="line">48</span><br><span class="line">49</span><br><span class="line">50</span><br><span class="line">51</span><br><span class="line">52</span><br><span class="line">53</span><br><span class="line">54</span><br><span class="line">55</span><br><span class="line">56</span><br><span class="line">57</span><br><span class="line">58</span><br><span class="line">59</span><br><span class="line">60</span><br><span class="line">61</span><br><span class="line">62</span><br><span class="line">63</span><br><span class="line">64</span><br><span class="line">65</span><br><span class="line">66</span><br><span class="line">67</span><br><span class="line">68</span><br><span class="line">69</span><br><span class="line">70</span><br><span class="line">71</span><br><span class="line">72</span><br><span class="line">73</span><br><span class="line">74</span><br><span class="line">75</span><br><span class="line">76</span><br><span class="line">77</span><br><span class="line">78</span><br><span class="line">79</span><br><span class="line">80</span><br><span class="line">81</span><br><span class="line">82</span><br><span class="line">83</span><br><span class="line">84</span><br><span class="line">85</span><br><span class="line">86</span><br><span class="line">87</span><br><span class="line">88</span><br><span class="line">89</span><br><span class="line">90</span><br><span class="line">91</span><br><span class="line">92</span><br><span class="line">93</span><br><span class="line">94</span><br><span class="line">95</span><br><span class="line">96</span><br><span class="line">97</span><br><span class="line">98</span><br><span class="line">99</span><br><span class="line">100</span><br><span class="line">101</span><br><span class="line">102</span><br><span class="line">103</span><br><span class="line">104</span><br><span class="line">105</span><br><span class="line">106</span><br><span class="line">107</span><br><span class="line">108</span><br><span class="line">109</span><br><span class="line">110</span><br><span class="line">111</span><br><span class="line">112</span><br><span class="line">113</span><br><span class="line">114</span><br><span class="line">115</span><br><span class="line">116</span><br><span class="line">117</span><br><span class="line">118</span><br><span class="line">119</span><br><span class="line">120</span><br><span class="line">121</span><br><span class="line">122</span><br><span class="line">123</span><br><span class="line">124</span><br><span class="line">125</span><br><span class="line">126</span><br><span class="line">127</span><br><span class="line">128</span><br><span class="line">129</span><br><span class="line">130</span><br><span class="line">131</span><br><span class="line">132</span><br><span class="line">133</span><br><span class="line">134</span><br><span class="line">135</span><br><span class="line">136</span><br><span class="line">137</span><br><span class="line">138</span><br><span class="line">139</span><br><span class="line">140</span><br><span class="line">141</span><br><span class="line">142</span><br><span class="line">143</span><br><span class="line">144</span><br><span class="line">145</span><br><span class="line">146</span><br><span class="line">147</span><br><span class="line">148</span><br><span class="line">149</span><br><span class="line">150</span><br><span class="line">151</span><br><span class="line">152</span><br><span class="line">153</span><br><span class="line">154</span><br><span class="line">155</span><br><span class="line">156</span><br><span class="line">157</span><br><span class="line">158</span><br><span class="line">159</span><br><span class="line">160</span><br><span class="line">161</span><br><span class="line">162</span><br><span class="line">163</span><br><span class="line">164</span><br><span class="line">165</span><br><span class="line">166</span><br><span class="line">167</span><br><span class="line">168</span><br><span class="line">169</span><br><span class="line">170</span><br><span class="line">171</span><br><span class="line">172</span><br><span class="line">173</span><br><span class="line">174</span><br><span class="line">175</span><br><span class="line">176</span><br><span class="line">177</span><br><span class="line">178</span><br><span class="line">179</span><br><span class="line">180</span><br><span class="line">181</span><br><span class="line">182</span><br><span class="line">183</span><br><span class="line">184</span><br><span class="line">185</span><br><span class="line">186</span><br><span class="line">187</span><br><span class="line">188</span><br><span class="line">189</span><br></pre></td><td class="code"><pre><span class="line"><span class="comment">// this指向案例31 - N;</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 31、call碰上箭头函数</span></span><br><span class="line"><span class="comment">// 箭头函数由于没有this，不能通过call/apply/bind来修改this指向，</span></span><br><span class="line"><span class="comment">// 但可以通过修改外层作用域的this来达成间接修改</span></span><br><span class="line"><span class="keyword">var</span> name = <span class="string">&#x27;window&#x27;</span>;</span><br><span class="line"><span class="keyword">var</span> obj1 = &#123;</span><br><span class="line">  <span class="attr">name</span>: <span class="string">&#x27;obj1&#x27;</span>,</span><br><span class="line">  <span class="attr">intro</span>: <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    <span class="keyword">return</span> <span class="function">() =&gt;</span> &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    &#125;;</span><br><span class="line">  &#125;,</span><br><span class="line">  <span class="attr">intro2</span>: <span class="function">() =&gt;</span> &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    <span class="keyword">return</span> <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    &#125;;</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">var</span> obj2 = &#123;</span><br><span class="line">  <span class="attr">name</span>: <span class="string">&#x27;obj2&#x27;</span></span><br><span class="line">&#125;;</span><br><span class="line">obj1.<span class="property">intro</span>.<span class="title function_">call</span>(obj2)(); <span class="comment">// obj2 obj2</span></span><br><span class="line">obj1.<span class="title function_">intro</span>().<span class="title function_">call</span>(obj2); <span class="comment">// obj1 obj1</span></span><br><span class="line">obj1.<span class="property">intro2</span>.<span class="title function_">call</span>(obj2)(); <span class="comment">// window window</span></span><br><span class="line">obj1.<span class="title function_">intro2</span>().<span class="title function_">call</span>(obj2); <span class="comment">// window obj2</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 32、箭头函数扩展</span></span><br><span class="line"><span class="comment">// 不可以用作构造函数，不能使用new命令，否则会报错</span></span><br><span class="line"><span class="comment">// 箭头函数没有arguments对象，如果要用，使用rest参数代替</span></span><br><span class="line"><span class="comment">// 不可以使用yield命令，因此箭头函数不能用作Generator函数</span></span><br><span class="line"><span class="comment">// 箭头函数没有prototype属性</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 避免使用场景</span></span><br><span class="line"><span class="comment">// (1)箭头函数定义对象方法</span></span><br><span class="line">name = <span class="string">&#x27;window&#x27;</span>;</span><br><span class="line"><span class="keyword">const</span> zc = &#123;</span><br><span class="line">  <span class="attr">name</span>: <span class="string">&#x27;zc&#x27;</span>,</span><br><span class="line">  <span class="attr">intro</span>: <span class="function">() =&gt;</span> &#123;</span><br><span class="line">    <span class="comment">// this -&gt; window</span></span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line">zc.<span class="title function_">intro</span>(); <span class="comment">// window</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// (2)箭头函数不能作为构造函数</span></span><br><span class="line"><span class="keyword">const</span> <span class="title function_">User</span> = (<span class="params">name, age</span>) =&gt; &#123;</span><br><span class="line">  <span class="variable language_">this</span>.<span class="property">name</span> = name;</span><br><span class="line">  <span class="variable language_">this</span>.<span class="property">age</span> = age;</span><br><span class="line">&#125;;</span><br><span class="line">lh = <span class="keyword">new</span> <span class="title class_">User</span>(<span class="string">&#x27;lh&#x27;</span>, <span class="number">24</span>); <span class="comment">// User is not a constructor</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// (3)事件的回调函数</span></span><br><span class="line"><span class="comment">// DOM中事件的回调函数中this已经封装了回调元素，</span></span><br><span class="line"><span class="comment">// 如果使用构造函数，其this会指向window对象</span></span><br><span class="line"><span class="variable language_">document</span>.<span class="title function_">getElementById</span>(<span class="string">&#x27;btn&#x27;</span>).<span class="title function_">addEventListener</span>(<span class="string">&#x27;click&#x27;</span>, <span class="function">() =&gt;</span> &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span> === <span class="variable language_">window</span>); <span class="comment">// true</span></span><br><span class="line">&#125;);</span><br><span class="line"><span class="comment">// 33、对象综合题</span></span><br><span class="line"><span class="keyword">var</span> name = <span class="string">&#x27;window&#x27;</span>;</span><br><span class="line"><span class="keyword">var</span> user1 = &#123;</span><br><span class="line">  <span class="attr">name</span>: <span class="string">&#x27;user1&#x27;</span>,</span><br><span class="line">  <span class="attr">foo1</span>: <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">  &#125;,</span><br><span class="line">  <span class="attr">foo2</span>: <span class="function">() =&gt;</span> <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>),</span><br><span class="line">  <span class="attr">foo3</span>: <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="keyword">return</span> <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    &#125;;</span><br><span class="line">  &#125;,</span><br><span class="line">  <span class="attr">foo4</span>: <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="keyword">return</span> <span class="function">() =&gt;</span> &#123;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">name</span>);</span><br><span class="line">    &#125;;</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">var</span> user2 = &#123; <span class="attr">name</span>: <span class="string">&#x27;user2&#x27;</span> &#125;;</span><br><span class="line">user1.<span class="title function_">foo1</span>(); <span class="comment">// user1</span></span><br><span class="line">user1.<span class="property">foo1</span>.<span class="title function_">call</span>(user2); <span class="comment">//user2</span></span><br><span class="line"></span><br><span class="line">user1.<span class="title function_">foo2</span>(); <span class="comment">// window</span></span><br><span class="line">user1.<span class="property">foo2</span>.<span class="title function_">call</span>(user2); <span class="comment">// window</span></span><br><span class="line"></span><br><span class="line">user1.<span class="title function_">foo3</span>()(); <span class="comment">// window</span></span><br><span class="line">user1.<span class="property">foo3</span>.<span class="title function_">call</span>(user2)(); <span class="comment">// window</span></span><br><span class="line">user1.<span class="title function_">foo3</span>().<span class="title function_">call</span>(user2); <span class="comment">// user2</span></span><br><span class="line"></span><br><span class="line">user1.<span class="title function_">foo4</span>()(); <span class="comment">// user1</span></span><br><span class="line">user1.<span class="property">foo4</span>.<span class="title function_">call</span>(user2)(); <span class="comment">// user2</span></span><br><span class="line">user1.<span class="title function_">foo4</span>().<span class="title function_">call</span>(user2); <span class="comment">// user1</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 34、隐式绑定丢失</span></span><br><span class="line"><span class="keyword">var</span> x = <span class="number">10</span>;</span><br><span class="line"><span class="keyword">var</span> foo = &#123;</span><br><span class="line">  <span class="attr">x</span>: <span class="number">20</span>,</span><br><span class="line">  <span class="attr">bar</span>: <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="keyword">var</span> x = <span class="number">30</span>;</span><br><span class="line">    <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">x</span>);</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line">foo.<span class="title function_">bar</span>(); <span class="comment">// 20 隐式绑定</span></span><br><span class="line">foo.<span class="title function_">bar</span>(); <span class="comment">// 20</span></span><br><span class="line"><span class="comment">// 有关运算符优先级的知识，成员访问与函数调用优先级相同，</span></span><br><span class="line"><span class="comment">// 默认从左到右，因此括号可有可无</span></span><br><span class="line">(foo.<span class="property">bar</span> = foo.<span class="property">bar</span>)(); <span class="comment">// 10</span></span><br><span class="line">(foo.<span class="property">bar</span>, foo.<span class="property">bar</span>)(); <span class="comment">// 10</span></span><br><span class="line"><span class="comment">// 隐式绑定丢失,起函数别名,将逗号表达式的值(第二个foo.bar)</span></span><br><span class="line"><span class="comment">// 赋值给新变量，之后执行新变量所指向的函数，</span></span><br><span class="line"><span class="comment">// 默认绑定，打印10</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 隐式绑定有个定性条件，就是要满足XXX.fn()格式，</span></span><br><span class="line"><span class="comment">// 如果破坏了这种格式，一般隐式绑定都会丢失</span></span><br><span class="line"><span class="comment">// 35、arguments(推荐看)</span></span><br><span class="line"><span class="keyword">var</span> length = <span class="number">10</span>;</span><br><span class="line"><span class="keyword">function</span> <span class="title function_">fn</span>(<span class="params"></span>) &#123;</span><br><span class="line">  <span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">this</span>.<span class="property">length</span>);</span><br><span class="line">&#125;</span><br><span class="line"><span class="keyword">var</span> obj = &#123;</span><br><span class="line">  <span class="attr">length</span>: <span class="number">5</span>,</span><br><span class="line">  <span class="attr">method</span>: <span class="keyword">function</span> (<span class="params">fn</span>) &#123;</span><br><span class="line">    <span class="title function_">fn</span>();</span><br><span class="line">    <span class="variable language_">arguments</span>[<span class="number">0</span>]();</span><br><span class="line">  &#125;</span><br><span class="line">&#125;;</span><br><span class="line">obj.<span class="title function_">method</span>(fn, <span class="number">1</span>); <span class="comment">// 10 2</span></span><br><span class="line"><span class="comment">// 将arguments[0]()展开看看</span></span><br><span class="line"><span class="comment">// arguments: &#123;</span></span><br><span class="line"><span class="comment">//   0: fn,</span></span><br><span class="line"><span class="comment">//   1: 1,</span></span><br><span class="line"><span class="comment">//   length: 2</span></span><br><span class="line"><span class="comment">// &#125;</span></span><br><span class="line"><span class="comment">// 36、压轴题(推荐看)</span></span><br><span class="line"><span class="keyword">var</span> number = <span class="number">5</span>;</span><br><span class="line"><span class="keyword">var</span> obj = &#123;</span><br><span class="line">  <span class="attr">number</span>: <span class="number">3</span>,</span><br><span class="line">  <span class="attr">fn</span>: (<span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">    <span class="keyword">var</span> number;</span><br><span class="line">    <span class="variable language_">this</span>.<span class="property">number</span> *= <span class="number">2</span>;</span><br><span class="line">    number = number * <span class="number">2</span>;</span><br><span class="line">    number = <span class="number">3</span>;</span><br><span class="line">    <span class="keyword">return</span> <span class="keyword">function</span> (<span class="params"></span>) &#123;</span><br><span class="line">      <span class="keyword">var</span> num = <span class="variable language_">this</span>.<span class="property">number</span>;</span><br><span class="line">      <span class="variable language_">this</span>.<span class="property">number</span> *= <span class="number">2</span>;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(num);</span><br><span class="line">      number *= <span class="number">3</span>;</span><br><span class="line">      <span class="variable language_">console</span>.<span class="title function_">log</span>(number);</span><br><span class="line">    &#125;;</span><br><span class="line">  &#125;)()</span><br><span class="line">&#125;;</span><br><span class="line"><span class="keyword">var</span> myFun = obj.<span class="property">fn</span>;</span><br><span class="line">myFun.<span class="title function_">call</span>(<span class="literal">null</span>); <span class="comment">// 10 9</span></span><br><span class="line"><span class="comment">// fn.call(null)或者fn.call(undefined)都相当于fn()</span></span><br><span class="line"><span class="comment">// myFun.call(null)：相当于myFun()，隐式绑定丢失，myFun的this指向window</span></span><br><span class="line"><span class="comment">// obj.fn为立即执行函数，默认绑定，this指向window</span></span><br><span class="line"><span class="comment">// 此时的obj可以类似的看成以下代码(注意存在闭包)</span></span><br><span class="line"><span class="comment">// obj = &#123;</span></span><br><span class="line"><span class="comment">//   number: 3,</span></span><br><span class="line"><span class="comment">//   fn: function () &#123;</span></span><br><span class="line"><span class="comment">//     var num = this.number;</span></span><br><span class="line"><span class="comment">//     this.number *= 2; // window.number = 20</span></span><br><span class="line"><span class="comment">//     console.log(num); // 10</span></span><br><span class="line"><span class="comment">//     number *= 3;</span></span><br><span class="line"><span class="comment">//     console.log(number); // 9</span></span><br><span class="line"><span class="comment">//   &#125;,</span></span><br><span class="line"><span class="comment">// &#125;;</span></span><br><span class="line"></span><br><span class="line">obj.<span class="title function_">fn</span>(); <span class="comment">// 3 27</span></span><br><span class="line"><span class="comment">// 隐式绑定，fn的this指向obj</span></span><br><span class="line"><span class="keyword">var</span> num = <span class="variable language_">this</span>.<span class="property">number</span>;</span><br><span class="line"><span class="variable language_">this</span>.<span class="property">number</span> *= <span class="number">2</span>; <span class="comment">// obj.number *= 2 = 6</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(num); <span class="comment">// 3</span></span><br><span class="line">number *= <span class="number">3</span>; <span class="comment">// 9 * 3 = 27</span></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(number); <span class="comment">// 27</span></span><br><span class="line"></span><br><span class="line"><span class="variable language_">console</span>.<span class="title function_">log</span>(<span class="variable language_">window</span>.<span class="property">number</span>); <span class="comment">// 20</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 为什么myFun.call(null)执行是，找不到number变量，</span></span><br><span class="line"><span class="comment">// 是去找立即执行函数AO中的number，而不是找window.number</span></span><br><span class="line"><span class="comment">// JavaScript采用的静态作用域，当定义函数后，作用域链就已经定死</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 隐式绑定：满足XXX.fn()格式，fn的this指向XXX。</span></span><br><span class="line"><span class="comment">// 如果存在链式调用，this永远指向最后调用它的那个对象</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 隐式绑定丢失：起函数别名，通过别名运行；函数作为参数会造成隐式绑定丢失</span></span><br><span class="line"></span><br><span class="line"><span class="comment">// 显示绑定：通过call/apply/bind修改this指向</span></span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"></span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"></span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"></span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"></span><br></pre></td></tr></table></figure>

<figure class="highlight javascript"><table><tr><td class="gutter"><pre><span class="line">1</span><br></pre></td><td class="code"><pre><span class="line"></span><br></pre></td></tr></table></figure>
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  2.  script[data-pjax]
  3.  .pjax-reload script
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<script>
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          "#l_main",
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